Test cricket is a complex sport, perhaps one of the most complicated ones out there, but at its heart a lot of it revolves around the top of off stump. Any bowler - quick, slow, right-arm, left-arm - looks to end up at the top of off, asking a batsman to watch for the outside edge, while also protecting the stumps. The sheer physicality of fast bowling means a quick usually bowls spells that are around five overs long. Some of the best bowlers in the history of the game have been those who quickly figure out which length and line on a certain pitch will help them end up in the general area of top of off to about a set of stumps wide.

The more satisfactory spells of play in Test cricket are produced when a bowler gets that radar right and a watchful batsman looks to negate it: leaving balls outside the line of his right eye - left in the case of a left-hand batsman - and punishing the bowler when he falters in length or line, all the time waiting for him to tire physically or mentally or both. A small error from a bowler produces runs, something similar from the batsman can result in a wicket. Reverse swing, magic balls, unbelievable shots enrich the sport, but a large part of it is about this examination around top of off.

For one fast bowler going around today, the top of off is the top of the batsman's shoulder. A batsman can wear all the armour he wants but he will keep getting bounced; this is not about hurting him, this is about getting him to play a shot he can't control. This bowler's short leg and deep square leg can be slightly in front of the crease, affording him two other fielders behind square on the leg side. The bouncers are almost always between the chest and the head. The shots the batsman is left with - the hook, the ramp and the upper cut - are fraught with risk.

Then you think in terms of how many accurate quick bouncers a guy can bowl. Surely he will tire? Surely he will lose pace? Surely there will be bad balls? Neil Wagner, though, keeps coming, ball after ball, bouncer after bouncer, with intensity, turning the tables, asking the batsman how much patience and agility he has to keep avoiding the various bouncers, because hooking or ramping them with the fields he has is difficult. And he doesn't stop at five-over spells.

"For me, I pride myself in being someone who can do it ten overs on the trot," Wagner says. "I love bowling. Hopefully I stay fit and strong and my body allows me to do that. I have been doing it for a long period of time in my career, and I can keep going and keep continuing to do it."

"I had to learn how to bowl into the wind, do the hard yards, bowl heavy into the wicket. And love that job"

What if a batsman keeps ducking? "I have got to keep bowling it," Wagner says. "That's the toughest thing. That's when the test of patience comes in. That's why it is called Test cricket. The longer you can do it for, the harder it becomes for a batsman to keep ducking. Somewhere they have to play a shot or try to play a shot."

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Pitches in New Zealand don't deteriorate. They just keep getting better and better to bat on with early moisture going out. A Christchurch Test, against England in 2002, sums up conditions in New Zealand. England were bowled out for 228 in the first innings, but ended up setting New Zealand 550 to win, which they threatened to achieve, thanks to Nathan Astle's 222 off 168 balls on a final-day pitch.

Twelve years later, on a similar flat track in Auckland, India were gunning down the 407-run target after having scored just 202 in the first innings. Shikhar Dhawan and Virat Kohli were chasing it almost like in an ODI. With India 218 for 2 in 60 overs and with Dhawan past a hundred and Kohli 50, New Zealand's only chance was the second new ball. Sixty runs had come from the last ten overs, 23 off the last two. There was a good chance there might not be enough left to defend when the new ball arrived.

The ball went to Wagner. It was his job to keep the scoring down and keep New Zealand in with a chance. He had gone for only 29 in 13 overs till then. That had been his job. To bowl heavy and dry outside off and try to frustrate the batsmen so that Trent Boult and Tim Southee could feed off it.

When Kohli cover-drove the first ball of Wagner's new spell, the 61st over, for four, Wagner went into his zone ("When the wicket is flat or the ball is not swinging or the batters are in and feeling comfortable"), almost an altered state of mind because what followed was not sane. In the spell of ten overs, he screamed into a heavy wind, bowled 18 bouncers, took the wickets of Kohli and Dhawan with two of them, conceded 26 runs, and gave the big boys vulnerable new batsmen against the new ball. The new Kookaburra swung for about ten overs, in which Southee and Boult took three wickets, but New Zealand still had MS Dhoni to contend with.

Shikhar Dhawan was out to a terrific bouncer on 115 Associated Press

Again they went to Wagner, who ripped out two wickets with no assistance from the pitch. On a weekday when the Indian supporters outnumbered fans of the host team, Wagner charged in tirelessly and produced four wickets out of nowhere in a sport that is heavily reliant on the surface, the overheads, or the uneven weight distribution on the ball. On a flat pitch on a sunny day with no reverse swing, Wagner willed New Zealand to win a Test amid boos every time he ended up next to the batsman in his follow-through after bowling a bouncer. "To see the way he looks back at me or if he is comfortable or not. And just to obviously have a bit of presence. Have them know I am there and I am going to come hard again."

When the ESPNcricinfo Awards were conceptualised in 2007, they were a unique concept in a sport dominated by aggregate numbers. These identified not the best batsman or bowler over the year but the single best individual performances. Wagner's Auckland effort made it to the longlist of 22 but didn't feature in the 12 nominees for the 2014 Test bowling award.

It perhaps sums up Wagner. He is somebody who bowls into the wind, when the ball is not new and when the pitch is not doing anything. He keeps the runs down so that the wicket-takers can strike. He is the dirty-pitch bowler who loses out to Doug Bracewell or the other exciting younger talent when New Zealand play on a greentop. His contribution reflects in the figures of others, and he gets to play when there is no assistance for the bowlers.

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When Wagner was just out of school, back in Pretoria, where he was born, he took up volunteer duties in a Centurion Test. He also got to field as a substitute and bowl in the nets. Shaun Pollock remembers him as a line-and-length swing bowler.

"McCullum is that sort of friend, that sort of captain, that sort of bloke that you feel you want to break the wall down for"

"Going to New Zealand, wickets became a lot flatter and slower," Wagner says. "Obviously wind became a factor.

"You bowl in a lot of strong winds. I had to try and look at different ways of making it to the team because we had quality swing bowlers in the team, like Tim, Trent, high-class swing bowlers. I wanted to bring something different to the team, in some different sort of way.

"At that time I had to learn how to bowl into the wind, do the hard yards, bowl heavy into the wicket. And love that job. With that started learning new skills. Started becoming a bowler who tries to be aggressive and bowl a few short balls and hit the wicket hard and not afraid to change something up to try and buy a wicket. Or create something.

"And I pride myself in when it is tough and if conditions are hard, I want to stand up and make the difference. It doesn't always happen, it is cricket, but on the day when it does come off, it feels great. Be as aggressive as I can be."

It is clear Wagner looks forward to things other bowlers dread: flat pitch, no overheads, semi-new ball. That is when you enter his playground. It's not pretty. It doesn't follow the rhythms of Test cricket. The seam doesn't come out right. The fields look strange at times. He bowls from extreme angles. He doesn't move the ball. He should be easy to see off but he isn't. He messes with your footwork. And if you are looking to see him off, he just keeps coming at you for ten-over spells. He is just an annoying bowler to face, the chaotic Mick Foley in a world of more technical wrestlers.

It doesn't come easy. "A lot of fitness and gym work," Wagner says. "Thanks to our trainer, Chris Donaldson. He has put a lot of hard work in it. You have to be fit and strong to look after your body.

Neil Wagner celebrates the win with his team-mates Getty Images

"I love bowling. I have got a massive love for cricket. For me to get the opportunity to play for New Zealand, to represent New Zealand, is a big honour. I play with a lot of passion. I love playing for the Fern. And for my team-mates. Love having that opportunity when times are tough and you have to stand up and create something special and do something for the team. Love that sort of moments."

Of course it doesn't always come off - else, his average would be 15 as opposed to 29.63. There are days when it does, like when he took five Australian wickets with bouncers in Christchurch. Only one of them was edged. So persistent and annoying had Wagner been that the Australia batsmen were forced to play shots that had a high probability of going to the fielders on the full. Even if you hit down on head-high bouncers, it is a long way down.

This was Brendon McCullum's last Test, the man instrumental in making Wagner the bowler he became.

"Brendon was outstanding," Wagner says. "He is such a smart cricket brain. Such a good head to read the game and see something before it sort of happened or unfolded. He was really good in giving you confidence. To do a certain role or certain plan and go with it. With those plans that came out, he asked me to do that job.

"Earlier in my career I struggled to adapt to certain conditions, certain wickets, or certain roles that I had to play. Trying to swing the ball and it wasn't swinging. And when it wasn't swinging, searching for swing and losing your shape. And your seam position. And then you end up forcing the ball, trying to bowl too quick, you miss your length. Became a thing when you put yourself under pressure early in the game, you felt like you had to play catch-up cricket.

"You don't want to let your team-mates down, so you try too hard. It was a hard time. When you don't have control over the ball. And then I had to really work hard on my wrist position. I had to bring something different to my game, and that was the bouncer. I had to bring something different to be able to question the batsmen's footwork."

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Wagner is not an unskilled henchman; his skill is different. When he got Dhawan and Dhoni out in Auckland, he went round the wicket to create an extreme angle. For Dhawan a throat-high bouncer arrived from his blind spot outside leg and made him fend. To Dhoni, Wagner went the widest any man has ever gone without bowling a no-ball. Wagner's foot landed inside the return crease, but the little toe was probably a fraction over. Dhoni had to play at the ball.

"You can be a competitive cricketer at international level. It is not all about talent, it is not all about ability"

"It's tough [to go round the wicket]," Wagner says. "Obviously different to your natural over-the-wicket angle. Your body moves in different lines and different angles. I was told by Allan Donald as a young kid growing up that you are always going to have pain as a fast bowler, you are always going to have something that is sore, some sort of niggle. You are never going to play a 100% and feel a 100%. You know you have to bite through your teeth, and make sure you keep fighting.

"I think it's something I have trained a lot. I did it in T20 and one-day cricket as well. Try and vary the crease where I come from, where I bowl from. I do try and come very wide.

"I did watch one thing as a kid growing up - how bowlers use the crease. Looking at Makhaya Ntini, who came very wide on the crease and used the angles. I tried in training to go as wide as I could on that crease. Trying to know where the crease is when I am bowling. Something I really worked hard on and trained, and try to make sure you don't bowl no-balls."

There is, in Wagner's case, as is often required of fast bowlers, a keen eye and a sharp brain. Once during a Dunedin Test, again on a flat pitch on fourth day, he had Angelo Mathews on the hop with a 70-over-old ball. It was the final day, and New Zealand needed to get past Mathews. Wagner noticed Mathews was moving across to get inside the line of the short balls and bunting them into the leg side. So this time the sucker ball was not a wide length one but a searing full ball at the base of the leg stump. Mathews gone, the big boys again cleaned up the rest with the new ball.

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Wagner and Mitchell McClenaghan are similar bowlers in a way. McClenaghan is used to shake things up with his uncomfortable lengths in ODIs when the pitches flatten out. He had to become that bowler because he couldn't get a place as a swing bowler ahead of Boult and Southee. Wagner performs that role in Tests.

McClenaghan says his motivation has always been to prove people wrong because he had been knocked down at many levels. Never selected for age-group teams, released from first-class sides, never felt valued. He wanted to prove everybody wrong.

Mike Hesson congratulates Neil Wagner on New Zealand's victory Getty Images

"I wouldn't say I wanted to prove people wrong," Wagner says. "I wanted to show people that anything is possible. You might not be the highest skilled cricketer or the most talented cricketer, but if you keep working hard and put a lot of heart and effort to it and put your mind to it and play with passion, you can go that extra step. You can be a competitive cricketer at international level. It is not all about talent, it is not all about ability."

As a schoolkid in Pretoria - he went to the same school as Faf du Plessis, a friend, and AB de Villiers - Wagner had two problems. He wanted to play at the highest level, and he couldn't even get into the Titans squad because it meant going past Dale Steyn, Andre Nel, the Morkel brothers and Alfonso Thomas. So he left Pretoria, and South Africa, for England, where he happened to be spotted by Mike Hesson, then the Otago coach.

"I wanted to make my family and my wife and my friends proud and myself proud, and I wanted to see what I could do," Wagner says. "It wasn't the easiest thing, to pack your bags up and say goodbye to your parents and see them once a year. As a young kid, taking all this stuff and leaving with no money in your bank…"

Hesson remembers the conversation when he asked Wagner if he would be interested to play for Otago. Hesson says not once did Wagner ask how much he would be paid.

"Money is not a question for me," Wagner says. "It is nothing.

"I have a lot of passion for the game. Obviously you have got to put a roof over your head and look after yourself and your career, but for me it was all about getting an opportunity to play international cricket. It wasn't anything to do with anything else. It was just that I had the aspiration to play at the highest level. I would do whatever it took at that time to do it.

"I had a high passion for New Zealand at that time - New Zealand sport and especially New Zealand rugby. When he [Hesson] asked me to come to New Zealand, the easiest answer was to say yes and go and try to further my cricket career. I have never looked back since."

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If he does look back, Wagner will find an impatient young man, dismissed as a "pretty boy" by some of his team-mates in Pretoria, who left the country complaining about the quotas. He will look back at a 22-year-old with no money landing up in a house he shared with strangers in Dunedin. Adjusting to the cold. Missing his brothers' weddings - the brothers who made him bowl for hours on end in the backyard. Missing his best friends' weddings. A 22-year-old not liked that much in his new team because in his first season it became "all about Neil", according to Hesson, after Wagner led the wickets chart for Otago. Perhaps now he is better placed to appreciate the merits of positive reinforcement than as a 22-year-old who wanted just one thing: international cricket.

"I was told by Allan Donald as a young kid growing up that you are always going to have pain as a fast bowler"

Wagner had people back home to prove wrong. He had a new country and new teams that he needed to be accepted in. Even as a New Zealand player, once, the story goes, he was asked to move out of the frame for a picture at an awards function because three "originals" wanted to be photographed together. That after he had served four years before becoming eligible to play for New Zealand. After the second year, Hesson says Wagner started to work really hard. Before he qualified for New Zealand selection, five wickets in an over in a first-class match in 2011 made sure everyone knew about him.

A "pretty boy" in a new land, seeking acceptance, having turned his life upside down, it is no surprise Wagner was prepared to do anything to be able to play cricket at the highest level. "Vaggner" had now become Wagner.

Now he is anything but a pretty boy of pace bowling. He doesn't bowl magic balls. He doesn't swing it around corners. He doesn't often send stumps cartwheeling; sometimes he can go entire spells without intending to hit them. He just keeps running, chest jutting out, ball after ball, basking in being an uncomfortable presence. Yet, having taken 99 wickets in 25 Tests, he is set to become the second fastest New Zealand bowler to 100 Test wickets. The great Richard Hadlee got there in 25. Wagner will be one of only 14 men to take 100 wickets for New Zealand.

"Never in my wildest dream [thought of 100 wickets]," Wagner says. "Tim and Trent are high-class bowlers. I just love watching them bowl. They have got phenomenal skill. Skill I wish I had. When I bowl, what I do is just to do whatever the team requires on that day. Every wicket I can take, if it is one or ten or five, for my team to contribute in some sort of way, I am happy to do it. Even if I don't take a wicket on the day, if I can create the pressure and not go for runs, do something for whoever it is at the other side, if I can play a part in them taking a wicket, I am more than happy."

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Wagner is a more rounded bowler now. He spent a year at Lancashire - breaking the record for the best debut there - working on his swing, bowling alongside James Anderson at times. He has worked hard on his wrist position.

Although he is not necessarily assured of a place in the 1st XI, he doesn't now always need a flat pitch to be playing. Every now and then he comes up against South Africa, and is told by Steyn that he is not courageous enough because he scores 31 off 30 batting at No. 10, as opposed to hanging around for 80 balls to see Kane Williamson through to a hundred.

Fast bowling is not a natural act; human bodies were not meant to do it. I ask Wagner if he considers himself an unfriendly, unpleasant presence on the field. "I have played against some of my best friends in cricket games," he says. "That's the biggest battles, against your best friends. As soon as you walk over the boundary rope, it is a battlefield. You representing your team and your country against the opposition. I play as hard as I can."

In this faux war, his general gave Wagner the biggest endorsement. "He epitomised everything we want to be known for as a team," McCullum said after the Auckland win against India. "He did it in a crunch moment as well. How aggressive he is, how hostile he is when he has got ball in hand, and how big his heart is as well. He bowled ten overs into the wind late on day four, which is no easy feat, and it allowed Tim and Trent to have some decent downtime leading into that new ball. He has bowled like that for us now for 12-18 months, and he hasn't always got the rewards. It was just nice today for a guy like that to get the rewards as well, and the accolades that follow.'

I read these words out to Wagner. "I get a bit of goosebumps when someone like that says something like this about you," he says. "He is that sort of friend, that sort of captain, that sort of bloke that you feel you want to break the wall down for."

Continents away from home, Wagner now has a team he can break the wall down for.