Son Heung-min joined Hamburg's youth academy as 16-year-old in 2008

Behind the endearing smile and elaborate handshakes lurks a man on a mission.

Son Heung-min's three goals against Manchester City in the Champions League quarter-finals helped fire Tottenham Hotspur into the last four of the competition for the first time in 57 years.

Back in 1962, with the competition in its former guise as the European Cup, Spurs were knocked out by a Benfica side boasting Portugal great Eusebio, and the Premier League outfit will need to overturn a 1-0 deficit against a talented young Ajax team to avoid falling at the same hurdle this time around.

Tottenham's hopes in Amsterdam, it seems, appear to be pinned on the return of their talismanic South Korean, who was suspended for the first leg in north London last week and in the absence of top-scorer and England captain Harry Kane has become his side's go-to threat.

Son has scored half of Tottenham's goals in the Champions League knockout stages this season and his importance to Mauricio Pochettino's side was underlined by the fact Spurs only managed one shot on target in the first leg without him.

"The game at Manchester City - two shots, two goals," says former Hamburg youth-team coach Markus von Ahlen about Son's performance during Spurs' 4-3 loss in a dramatic quarter-final at Etihad Stadium that saw the visitors progress on away goals.

"You don't get many chances and you have to have the security to know if you have one chance you are going to make it."

Von Ahlen is well aware of the back story to Son's rise to prominence - it is one of persistent hard work, following the unconventional training methods of his disciplinarian father and having the bravery to move to another continent as a teenager in order to pursue his dream.

Von Ahlen worked with Son when he first arrived in Germany as a 16-year-old, having been scouted alongside two other players as part of a link between Hamburg and the South Korean Football Association.

"He was very quick, he scored a lot and he was very open in working with the team and very interested to learn things," Von Ahlen, who now works at Bayer Leverkusen, tells BBC Sport.

"His father was there also, and every minute he was free his father trained with him additionally - small, easy technical things. He worked every day."

Son Heung-min celebrates after scoring for Hamburg's youth team

Son has spoken openly about his father's impact on his career - from the strict training regimes he implemented on Son and his older brother as children, to still sharing a flat with his parents in London and being told he should not marry until his playing career is over.

Son Woong-jung was himself a professional footballer in South Korea, until injury curtailed his career in 1990 - two years before the younger of his sons was born.

When his boys were not studying - which included trips to a summer school in New Zealand to learn English - Woong-jung would put them through a strict footballing education of relentlessly practising basic skills.

The boys would have to master one attribute before moving on to the next, while Son recalls his father punishing him with hours of keepy-uppies.

Other punishments were harsher.

"I hit my sons a lot because sometimes it's necessary. I know Europeans don't understand this though," Woong-jung told Korean journalist Minhye Park external-link when she met him at the SON Football Academy in his home city of Chuncheon.

"It's a very usual practice and, especially in his case, it's done by parents," Park explains to BBC Sport. "It's more understandable from Koreans' viewpoint."

One of Woong-jung's more unconventional methods was to restrict shooting and passing drills and not let his sons play in matches until they were 14 years old.

"He thinks it can ruin the potential of the athletes by over-working their muscles," added Park. "He also thinks having practice games during training hurts the psychology of athletes."

When Son joined Hamburg, Von Ahlen said he was "technically good with both feet and his head" but it was his ferocious appetite for scoring goals that stood out to the former Leverkusen midfielder.

"We played 4-4-2 with two strikers in the centre and he played there, but at this age you saw it is possible for him to play on the wings," says Von Ahlen. "Now he is a very flexible player.

"What is special about him is the quickness and speed he has and then the character to want to make the goal, he absolutely wants to go to the goal and make the goal. You could see that at a young age."

Despite the disciplined approach, Son credits his father for providing the platform and support for him to become a professional, as well as instilling in him a humble and respectful nature.

"It was beautiful to work with him," adds Von Ahlen, who says it was quickly clear to the coaches at Hamburg that Son possessed the right attributes to forge a successful career.

"Every time I saw him in the morning he would laugh and he is very open. When I talked with him he thinks upwards. Every time, he doesn't say 'OK, I am happy to be in Hamburg' - at a young age, it was his dream to go to the Premier League.

"That is for me the special thing with Son. He talked about the Premier League and so his dream becomes truth - it is a thing of first having the talent, making the work and having the support, also a little bit of luck with injuries, but he had this vision and knew what he had to do and now he gets his dream."

Son during pre-season with Hamburg

In the decade since joining Hamburg as a teenager - breaking into the first team at 18 and joining Bayer Leverkusen before signing for Spurs - Son has established himself as arguably South Korea's greatest player of all time and become a national hero, helped by an obvious affection for his home country.

The 26-year-old has talked about how he feels like an ambassador for South Korea and has a responsibility to supporters who visit London just to watch him play, as well as those tuning in throughout the night to follow Tottenham games on television.

When Son returned home on a pre-season tour while with Leverkusen he discovered 30,000 fans gathered in a shopping centre waiting for him, according to his former team-mate Robbie Kruse, who told Australian newspaper the Herald Sun external-link it "blew the players' minds" and was like being out with a "rock star".

The national team captain now wears a baseball cap and sunglasses on visits as he worries about people being hurt in the large crowds that would otherwise follow him.

Meanwhile, after South Korea declared a national emergency in response to more than 4,000 people being evacuated because of large-scale wildfires last month, Son donated £100,000 to help the victims.

His stock is such that he currently tops a vote to be named as the cover star for Fifa 20 when the game is released later this year - racking up more than 240,000 nominations to lead from Cristiano Ronaldo and Lionel Messi - while last month he beat South Korean legend and former Bundesliga star Cha Bum-kun in a national popularity poll.

But his crowning glory with South Korea came in winning the Asian Games last September, guaranteeing an exemption from the two-year mandatory military service expected to be completed by his countrymen.

"Two years out of football finishes your career," remarked former Tottenham and South Korea defender Lee Young-pyo at the time, emphasising how important the army is to the nation.

Son burst into tears after the final whistle, but said it was because of the pride of achieving with his country rather than avoiding military service, which he would have had to return for at the age of 28, and told the Guardian external-link he still intends to complete a four-week soldier's training course.

Park says the number of people celebrating Son's military exemption was surprising and generated some "mixed patriotism" in South Korea.

"It was his leadership and sacrifice for the national team," she explains. "We are obsessed with attitudes, it's a cultural thing. In the past some athletes didn't show their gratitude or respect to the national flag.

"What Heung-min and his father were praised for after the Asian Games was their attitude in interviews when they were asked about his military exemption, because they gave all of this credit to the Korean people who cheered for them."

There was a time, after his first season at Tottenham, that Son was said to be considering his future at the club. Convinced to stay, he went on to score 21 times in all competitions during the 2016-17 campaign, 18 last term and already has 20 goals this season.

"Of course after the first season he understood what we expected of him," said Tottenham boss Pochettino.

"Now he's one of the players who is always moving on the pitch, trying to get the best position in defensive and offensive situations. Always giving options to team-mates, running forward, dropping and then arriving from the second line.

"He is a very complete player today and we are so happy with his performance."

And so to Wednesday at the Johan Cruyff Arena, where Tottenham's hopes of reaching a first Champions League final in the club's history could hinge on a player moulded in a vastly different manner to those of his team-mates.

"Son is one of the players who can make it possible for Tottenham," adds Von Ahlen. "For him I hope so, it is a beautiful feeling if you see one of your youth players make it this way."

One thing is certain, Son's many fans in South Korea will be rising early in the morning to follow their hero in the biggest game of his club career to date.

"It would be a national success," says Park. "It's like 'our' success."

Son was signed by Bayer Leverkusen in 2013, before moving to Tottenham two years later

Son is held aloft by his team-mates after South Korea win the gold medal at the Asian Games

Son's father, Son Woong-jung, at his academy in South Korea