This year, BBC Sport is profiling 20 of the greatest Formula 1 drivers of all time. The BBC F1 team were asked to provide their own personal top 20s, which were combined to produce a BBC list. Veteran commentator Murray Walker provides his own reflections in a video of their career highlights, and chief F1 writer Andrew Benson profiles the driver. This week, number three - Jim Clark

Jim Clark hated Spa. Even in its truncated modern form, the Belgian Grand Prix track is an extreme examination of man and machine, but back in Clark's era it was something else again.

At nine miles, it was more than twice its current length, with an average speed even in the early '60s of more than 130mph.

Then as now, it included some of the most testing corners on the planet. Eau Rouge was a far greater challenge than it is in the modern era, when the cars take it flat out, downforce ruling all.

But even Eau Rouge paled compared to the Masta Kink - a left-right between houses, flat-out at 160mph for only the very brave and very skilled.

It wasn't that Clark could not handle Spa; far from it. He was the greatest driver of his era by far. But he thought it dangerous in the extreme.

In the 1960 race, only Clark's second grand prix, Stirling Moss - whose mantle as the best of his time Clark would soon inherit - was badly injured in a crash in qualifying at the fast Burnenville right-hander.

Jim Clark factfile Born: 4 March 1936 in Fife, Scotland Died: 7 April 1968 aged 32 Races: 73 Wins: 25 First race: 1960 Dutch Grand Prix First win: 1962 Belgian Grand Prix Last win: 1968 South African Grand Prix Last race: 1968 South African Grand Prix

In the grand prix the next day, Clark very nearly ran over the beheaded body of Chris Bristow, killed in a crash at the same corner. Later in the race, Clark's team-mate Alan Stacey was killed at Malmedy.

These memories never left Clark, but a sense of his skill and commitment can be seen in the fact that he never let it affect his driving. Despite his aversion to the place, he won at Spa four times on the trot from 1962-5.

Among those victories was one that counts among his very best - and therefore, because of Clark's stature, among the greatest drives of all time.

Starting the 1963 Belgian Grand Prix only eighth in horrendously wet conditions, Clark quickly moved to the front. By the end of the race, only Jack Brabham had managed to stay on the same lap - and he was nearly five minutes behind.

In 1967, the Lotus 49, its powerful Cosworth engine in a league of its own, was the fastest car. But it was far from easy to drive. Yet at the German Grand Prix that year Clark was on pole by nine seconds.

Performances like that left no doubt in the minds of Clark's rivals about his status. He was out on his own, and they knew it.

"Jimmy was a demi-God," says Jean-Pierre Beltoise. "He was the best driver among us at that time."

Jackie Stewart, remembering a string of races in which he finished second to Clark, says: "We became known as Batman and Robin. And there was no doubt who was Batman and who was Robin."

It is worth taking a little time to appreciate the statistics of Clark's career.

His tally of 25 victories was a record at the time. It has since been surpassed by several other drivers, but none in so few races. Clark's came in just 72 starts, a win ratio surpassed only by Alberto Ascari and Juan Manuel Fangio.

Likewise, his tally of 33 pole positions was recently passed by Red Bull's Sebsatian Vettel, with only Michael Schumacher and Ayrton Senna ahead. But in percentage terms, Clark is ahead of them all. He was on pole for 45.2% of his races - only Fangio, on 55.8%, did better.

Those numbers give a sense of how Clark towered over his era, a period when he made many grands prix mind-numbingly boring, so completely did he and his Lotus dominate them. Yes, the Lotus was often the best car, but Clark's supremacy was not in doubt.

His two titles in 1963 and 1965 were exercises in crushing superiority, and he would have won in 1964 and 1967 as well had it not been for the notoriously poor reliability of Lotus's cars.

And if it had not been for Clark, Lotus may well not have won as many races as they did. Alongside his speed, Clark also had a rare ability to drive around problems. His smooth style took so little out of the car, a crucial skill with machinery as fragile as his.

The son of a farmer in the Scottish borders, Clark was a humble, quietly spoken man. But he had a dry wit, and he was well aware of the level of his ability.

A favourite anecdote is of a time Stewart was telling of a terrifying moment he had had when his throttle stuck open at Monza's Curva Grande - now just a bend in a straight and easily flat out; then a properly challenging high-speed corner.

Stewart related to his audience how he had somehow just made it around. There was a chorus of appreciation. Then, with immaculate timing, Clark said: "Are you saying, Jackie, that you normally lift off there?"

Clark's status among his fellow drivers was such that his death hit them particularly hard. The late 1960s was an era when driver fatalities were commonplace, but Clark was so good no-one thought it could happen to him.

It did, though. He won the first grand prix of 1968, in South Africa, but there was a four-and-a-half-month break between it and the next race in Spain. As was common in those days, Clark filled it by competing in other races.

That is how he ended up driving in a Formula Two race at a wet Hockenheim on 7 April 1968.

The Lotus, on Firestone tyres that were poor in the rain, was uncompetitive, and unusually for him Clark was neither a front-runner nor making ground on those who were.

Then something went wrong at the fast Ostkurve. There were no barriers and Clark's car plunged at full speed into the trees, where he was killed instantly.

For the other drivers, it was more than a shock.

"As well as the grief, there was another dimension altogether," said the New Zealander Chris Amon, who was behind Clark when he had his fatal crash, although he did not see it. "If it could happen to him, what chance did the rest of us have? I think we all felt that. It seemed that we'd lost our leader."

For Stewart, the pain was worse than for most. Even today, when he speaks about it, the anger and sense of monumental loss is barely disguised.

"Jim Clark died almost certainly because of a vehicle failure of some kind," Stewart told the BBC programme, 'Grand Prix, The Killer Years'. "There was no barrier, no fencing in front of a forest. And Jim Clark died violently in a forest, being hit by young trees and big trees alike, and his car was almost totally destroyed. And Jimmy died. It just was inconceivable."

Stewart had by then already started his campaign for increased safety in F1, and the death of his friend underlined to him just what an important task it was.

In the most tragic of circumstances, then, Clark helped define the future of the sport, as well as bestriding like a colossus part of its past.

Number 4 - Michael Schumacher

Number 5 - Alain Prost

Number 6 - Sir Stirling Moss

Number 7 - Sir Jackie Stewart

Number 8 - Sebastian Vettel

Number 9 - Niki Lauda

Number 10 - Fernando Alonso

Number 11 - Alberto Ascari

Number 12 - Gilles Villeneuve

Number 13 - Nigel Mansell

Number 14 - Mika Hakkinen

Number 15 - Lewis Hamilton

Number 16 - Nelson Piquet

Number 17 - Emerson Fittipaldi

Number 18 - Jack Brabham

Number 19 - Graham Hill

Number 20 - Jochen Rindt