There aren't many midfield destroyers who somehow get more terrifying when they retire.None of us would want to meet Roy Keane in a dark alley, let alone on a football pitch.Even 80s hard man Graeme Souness is quite obviously afraid of him. Every time he raises half a smile across the Sky Sports studio, the Liverpool legend is pleading with Keano not to hurt him.And speaking of Liverpool, they were the latest victims of the Irishman's acid tongue on Sunday, when he slammed them as "bad champions" who were full of "excuses" after losing 4-1 to Manchester City.Back in the day, of course, his fearsome reputation was forged in a Manchester United shirt.Only three players in Premier League history - Richard Dunne, Duncan Ferguson and Keane's nemesis, Patrick Vieira (who are all on eight) - received more red cards than him.Lee Cattermole, Vinnie Jones and Alan Smith were tied with him on seven acts of thuggery.It's unfair to lump him in with some of the top flight's more ill-disciplined midfielders, though. Keane was no shrinking violet, but he was an absolutely brilliant tackler too.p1eu40e6sq10p911vi13b01b84fjdj.jpgIt's easy to forget he ruptured his ACL in 1997, an injury which, prior to some of the latest medical advances, had the potential to ruin his career. Instead, he got better and better and played a key role in United's extraordinary treble win in 1999.Keane made 35 appearances in the Premier League and another seven in the FA Cup, but he didn't make it into the PFA Team of the Year. That's quite possibly because the 1998/99 edition already featured no fewer than five United players: Jaap Stam, Denis Irwin, Gary Neville, David Beckham and Dwight Yorke. But in the Champions League, Keane really started to get the credit he deserved. While he missed out on the final through suspension - as did Paul Scholes - he starred in the run to the final, helping Sir Alex Ferguson's men to overcome the likes of Barcelona, Brondy and Inter Milan. However, there was one performance which stood out above them all - his mesmerising display against Juventus in the semi-finals. United's official website even posed the question: "Was this the greatest individual United display?" It's certainly a valid debate, given the calibre of opponent Keane was up against - not least World Cup winner Zinedine Zidane, who was just a couple of years off earning his career-defining move to Real Madrid. Zizou could leave most midfielders lying in his wake, but even after realising Keane was gaining ground on him, he could do nothing to stop him executing a perfect tackle from behind. You can check it out here, at the very beginning of BT Sport's compilation of some of his best challenges: 

Sir Alex Ferguson famously hailed it as one of the best individual performances he'd seen.

“Pounding over every blade of grass, competing as if he would rather die of exhaustion than lose, he inspired all around him," Ferguson said. "I felt it was an honour to be associated with such a player.”