On 8 December 1999, at 8.23pm, I fell in love with another man. Roy Keane probably wouldn't care much for this revelation, but then I'm pretty sure I wasn't alone. The context was a long-forgotten match between Manchester United and Valencia in the long-forgotten second group stage of the Champions League. Long forgotten, that is, by everybody except those besotted with Roy Keane.

For the preceding five months, there was a serious danger that Keane, aged 28 and at the peak of his not inconsiderable powers, would leave United. His contract was due to expire in the summer of 2000, and United were unwilling to break their rigid wage structure to give Keane the £50,000 a week he wanted. Moves to Juventus and Bayern Munich were frequently discussed in the press; the Bosman rule meant that, as of 1 January 2000, Keane could discuss terms with foreign clubs. All that scaremongering about the Millennium Bug had nothing on the millennial angst felt around Old Trafford. The word 'unthinkable' does not begin to do justice to the thought of that United side without Keane. Impasses are usually tedious; this was terrifying.

Then, on the afternoon of United's match against Valencia, the club announced that Keane had signed a new contract. It was a match United had to win; they had lost the first group game away to Fiorentina, largely because of a rare and hideous error from Keane. A fortnight later he righted that wrong, slamming in a joyously emphatic opening goal from the edge of the area. Keane had already made far greater contributions for United, most famously away to Juventus in the previous season's semi-final, but the combination of the goal and the earlier defenestration of the desperate thought of a world without him made it a nigh-on perfect moment. The sort that makes you realise that, even when you grow old and doddery, and when you wouldn't recognise your other teenage heroes if they were stood in front of you holding a walking stick, you will still love Roy Keane.

There is something about Keane that inspires such extreme devotion – and also wonder. At the 2012 Soccer Aid event, superstars like Robbie Williams and Will Ferrell were clearly in awe of Keane. Most fans of big English clubs other than United hate him, of course, and in that respect Keane is an uber-Marmite figure: those who love him would generally be willing to go to the ends of the earth for any unspecified Keane-related purpose. As a player, he was of his time by not being of his time: he captured the pre-millennium angst of the outsider who cannot understand the world of which he is part. In doing so he brought to mind a number of pop-culture characters of a similar disposition. Two in particular: Tyler Durden in Fight Club and Tony Soprano in The Sopranos. Like Keane, both raged, raged against the dying of society's light. There are other similarities. The intense adoration Keane receives evokes that of Tyler Durden, while his obtuse charisma, anti-heroism and scattergun frustration is shared by Tony Soprano. Keane, like Soprano, was raging for a better world and a better him. He has always been an incredibly complex man, a compelling fusion of instinctive intelligence and pathological desire.

Keane, like Tony Soprano, is a mass of often uncomfortable contradictions. Thank goodness for that. The most interesting people in life are invariably flawed, and Keane has been the most interesting person in British football for the last few decades – an outsider even down to his Diadora boots, never mind the candour that is so rare in modern football. What kind of hero would you prefer? Prom kings are for dreamers and liars. Having Roy Keane as a hero allows a vicarious ride through life in all its miserable glory.

For all his success – Keane won seven Premier League, four FA Cups and, although he'd tell you otherwise, one European Cup at Manchester United – football has often been brutally unkind to him. He was booted out mercilessly by a club and manager to whom he had given his soul and body. He missed out on his only European Cup final because of suspension. A year later, when he seemed to be on a personal mission to win the trophy – he scored six Champions League goals that season, almost half his career total of 14, and played with almost demented purpose – he then scored an own goal and missed an open goal in the quarter-final defeat to Real Madrid. Having got Ireland to the World Cup in 2002 with arguably the greatest football of his career, he missed out on the tournament because of his infamous row with Mick McCarthy. Keane always defined himself and his teams by global competition; you only have to see his boyish excitement as he stood pitchside for ITV ahead of Milan v Barcelona to realise that. Despite playing some awe-inspiring football for Ireland and for United in Europe, he played just in just one major tournament and no European finals.

If this tells us of the essentially cruel nature of football, they will not necessarily be our abiding memories of Keane. We will remember him as somebody who personified leadership, who controlled games with forensic intelligence, who was a grossly underrated passer and who, on occasion, put the fear of God into both opponents and teammates. That was a consequence of an intractable obsession with excellence. Keane combined a higher state of concentration and an inhuman perfectionism to consistently reach a level of performance beyond almost anyone else – even if that level of performance regularly did not satisfy the critic within. He was not interested in glory. Glory was something that came if you did your job properly. That, nor heroism, interested him. "You can be a hero – whatever that is," he sniffed in his autobiography.

Players of Keane's type are regularly described as 'winners', and with good reason. Keane did not so much have a will to win as a need to win. "If I was putting Roy Keane out there to represent Manchester United on a one against one, we'd win the Derby, the National, the Boat Race and anything else," Sir Alex Ferguson once said. "It's an incredible thing he's got."

It was not just winning that interested Keane, however. He was equally concerned with excellence and personal pride; winning was usually the result of the exhibition of those qualities. It was not necessarily a deal-breaker. In his autobiography he talks about the performance that first caught the attention of Nottingham Forest scouts. His team were 5-0 down with a few minutes to go. Everybody else had waved the white flag, but Keane kept doing the right things: demanding possession, moving the ball on crisply, putting out fires when the opposition had the ball. The qualities were in evidence at Forest, too: in 1992-93, the first season of the Premier League, Keane fought a lone, heroic and ultimately doomed battle to keep Forest in the Premier League.

Keane detested mediocrity, and sometimes that need for excellence proved overwhelming. It is no coincidence that his infamous foul on Alf-Inge Haaland in 2001 came immediately after Manchester City had equalised at Old Trafford. United were already champions, but they had surrendered feebly in Europe to Bayern Munich earlier in the week and Keane was convinced they were in the comfort zone. When City – a poor side who would be relegated – equalised, it all bubbled over. Prawn sandwiches, mediocrity, couldn't even beat City at home, comfort zone, Haaland in possession. "Alfie was taking the piss". Bang. Haaland was toppled like a folding deckchair and Keane was the villain again.

Keane's detractors say he was little more than a thug who went round booting people at a time when the game's laws had not evolved sufficiently. This is such offensive poppycock that it barely merits mention. The primary weapons in Keane's arsenal, by a distance, were his energy, positional sense and game intelligence. Never was this more evident than during a magnificent performance in the 1996 FA Cup final against Liverpool. The game is remembered for Eric Cantona's masterful late winner, which clinched the Double for United and completed his fairytale; justly so, yet that goal was infinitesimal in the grand scheme. In this game, as much as any others, Keane's footballing philosophy emphatically came to pass.

This particular devil has always been obsessed with detail, and the minutiae of football matches. "They say God is in the detail; in football that's true," he said in his autobiography. "Sometimes games are won by a magical goal – that's what people remember. But the essence of the game is more mundane. Detail. Wearing down the opposition. Winning the psychological battles – man on man – from the moment the ref blows the whistle for the first time." Keane called it the Law of Cumulation. "First tackle, first pass, first touch, everything counts. A lot of little things add up to the thing that matters: breaking the opposition's hearts – but first their minds, their collective mind."

Liverpool were a dangerous, free-flowing side who created umpteen chances in the two league games against United that season: a 2-2 draw at Old Trafford and a 2-0 win at Anfield that could have been 8-0 but for Peter Schmeichel. Keane did not play at Anfield, but he grudgingly respected Liverpool's abundant attacking talent: Robbie Fowler, Jamie Redknapp and Steve McManaman all played the most progressive football of their career under Roy Evans. The unpredictable brilliance of Stan Collymore was also worthy of respect. Keane's fear of Liverpool's capabilities was accompanied by loathing. In short, he couldn't stand them. The notion of the Spice Boys was anathema. Lee Sharpe tells a story of him and an "absolutely smashed" Keane bumping into the Liverpool players in a bar one Saturday night. Keane went through them one by one, dismissing their England B caps, England under-21 caps and League Cup winners' medals. The gist, frequently expressed, was simple: "What the hell have you done in the game?"

Then they turned at Wembley in cream Armani suits. The FA Cup final had been turned into fancy dress day, a jolly boys' outing. You can only imagine the unremitting contempt on Keane's face as he looked those sartorial monstrosities up and down. With help from his trusted lieutenant Nicky Butt, Keane shut Liverpool down with remorselessness, concentration and intelligence. They had barely a chance all game. It was one of the great defensive-midfield performances. It meant the game, as hyped as any FA Cup final in the modern era, was a stinker, but are you going to tell Roy Keane that was a bad thing?

This is an extract from a chapter in Life's a Pitch: The Passions of the Press Box, which includes essays from 18 writers, including Dominic Fifield, Jonathan Wilson and Rory Smith, and a cover quote from Rafa Benitez: "These are the writers as you don't normally see them: when they are fans with pens."