By Phil McNulty
Chief football writer
Midfielder Keane bows out in his testimonial match
Roy Keane once announced with uncharacteristic understatement: "I'm not at Manchester United to keep everyone happy."
His departure from Old Trafford last November was proof of that.
Keane had barely half a season with his beloved Celtic but it was obvious a catalogue of serious injuries were beginning to take their toll and it was no real surprise when news of his retirement from the game came through.
Everyone who has come across the former Manchester United captain, worked with him, or played with and against him, can vouch for the fact he has never taken any prisoners.
Whether it's his old manager and mentor at United, Sir Alex Ferguson, fans, or various members of football's worldwide community - all have at one time or another fallen foul of this most driven of competitors.
And that's been primarily because of his relentless pursuit of perfection.
Keane made enemies in establishing himself as the man Ferguson rates as the greatest player of his Old Trafford reign.
But no-one with United's best interests at heart was happy to celebrate the exit of a legendary Old Trafford figure.
And the same can be said of the Celtic fans, 35,000 of who made the journey south for Keane's sell-out testimonial in May.
Ferguson rarely had cause to regret the day he took Keane from under the nose of a fuming Kenny Dalglish for £3.75m in July 1993, just as he was poised to join Blackburn from Nottingham Forest.
Keane came to embody Ferguson's own spirit inside Old Trafford - issuing his orders on the pitch and delivering public criticism that many suspected had been scripted by his manager.
He was central to Ferguson's whole football philosophy and was arguably the Premiership's finest midfield operator in the last decade.
They have a few drinks and probably the prawn sandwiches and don't realise what's going on out on the pitch. I don't think some people who come to Old Trafford can spell football, never mind understand it
On some of Man Utd's fans
The great teams get back to finals and win it, and this just shows we are not a great team. We're just an average team in a lot of areas
On his team-mates in 2001
Even in the dressing
room afterwards I had no remorse. What goes around comes around. He got his just rewards. My attitude is an eye for an eye
On his tackle on Alf Inge Haaland
This is something I'll remember for the rest of my life.
To Man Utd and Celtic fans after his sell-out testimonial
I've been fortunate to work under two of the game's great managers, in Brian Clough and Alex Ferguson, and the thought of being manager of Man Utd would be fantastic
Our performance levels have not been good enough. Everyone at this club needs to look at themselves and ask whether they are giving 100%
After failing to win a trophy in 2005
It is no coincidence that it has not just been the arrival of Roman Abramovich's chequebook at Chelsea that has resulted in United's failure to maintain their Premiership supremacy.
Keane's own declining powers and physical fitness were also a major factor in Ferguson's struggle to return the title to Old Trafford.
And Ferguson's failure to adequately address the issue of Keane's potential replacement was a huge flaw in his future planning.
As for Keane himself, spats and silverware have come in equal measure, his row with Republic of Ireland boss Mick McCarthy and a lack of repentance over a horror tackle on Alf Inge Haaland evidence of his darker side.
McCarthy was furious with his captain for walking out on the side at the start of the 2002 World Cup, saying: "I never want to see him again, never mind work with him."
Keane has also publicly lashed his own team-mates with strategically-timed attacks and his now-infamous attack on Old Trafford's "prawn sandwich" supporters created a new term in football's glossary.
And yet it was this verbal assault that cemented his status as United's man of the people, a player more at home with the fan on the street than in football's more corporate corridors.
For all that controversy, Keane deserves to bow out with his status as one of the game's greats unchallenged
He emerged at Nottingham Forest under Brian Clough as a wild, driving, goalscoring midfield man with huge untapped potential.
He started at Old Trafford in the shadow of Bryan Robson but soon emerged as the finished article, helped by the shrewd guidance of Ferguson.
And, showing an astute football brain, he tailored his style to adjust to the passage of time and the onset of injuries.
Recently he has been more a restrained holding player and enforcer rather than a rampaging force but still outstanding in his field, adding Scottish Premier League and CIS Cup winners' medals to his impressive collection.
But his finest hour arguably turned into his biggest disappointment.
No United fan will ever forget Keane's stunning performance against Juventus in the Champions League semi-final victory in Turin in 1999 - delivered after picking up a yellow card that ruled him out of the final against Bayern Munich.
As Ferguson knows only too well, Keane, is a man and player who will prove irreplaceable - on and off the pitch.