As players or personalities, Niall Quinn and Roy Keane share few similarities.
Quinn and Keane have had their differences
But the former Republic of Ireland team-mates, who had a spectacular falling out before the 2002 World Cup finals, have become unlikely bed-fellows at the Stadium of Light.
With Sunderland chairman Quinn appointing Keane as the manager to turn his struggling club around, BBC Sport takes a look at the history of the Black Cats' peculiar pairing.
Quinn is the genial giant who has laughed and joked his way through life. Keane is the angry ant who even when things were going well was never far away from a scowl.
During his spell as a Sunderland player, Quinn could often be found in a pub chatting to the locals about everything from horse racing to politics.
Keane preferred walking the dog to spending time with his team-mates
In contrast, Keane wanted nothing more than to be left alone to walk his dogs.
As a player, Quinn gained success through a deft touch and a fine reading of the game, happy to admit that he was never one of the most dedicated when it came to cross-country runs.
Keane was the fierce competitor, not content unless his team-mates were also squeezing out every last drop of effort.
Off the field, Quinn, seen as one of the brightest and most articulate of footballers, rarely had a bad word for anyone or anything, and few have had a bad word about him.
Keane is a man of few kind words, from managers to the media, from team-mates to opponents.
Even his own fans did not escape his wrath, with his famous "prawn sandwich" tirade about Manchester United's supporters.
WORLD CUP FINALS FALL-OUT
In the summer of 2002, Keane attracted criticism for skipping Quinn's testimonial in Sunderland.
The midfielder, who had refused to contribute to the programme notes for the game over a spat with a journalist, was injured but still expected to show his face.
In turn, Quinn was one of the senior players that Keane felt had refused to back him in his quest to improve Ireland's facilities.
But all that was just the eye of the storm that was to follow when Keane and Republic of Ireland manager Mick McCarthy fell out ahead of the World Cup finals in Japan.
Quinn found himself stuck in the middle of the Saipan controversy.
Quinn and Keane share an agent in Michael Kennedy and the big striker became a mediator in trying to broker a peace deal.
And when Quinn was ultimately forced to take sides he threw his backing behind manager McCarthy.
In Keane's eyes you are either with him or against him - and Quinn was very much against him.
Both Quinn and Keane aired their views through the media over the saga that split a nation.
Here's what they had to say about each other:
Keane on Quinn:
"Niall Quinn going on TV and saying that he was shattered from it, saying he hadn't slept. Did he think it was a walk in the park for me coming back to Ireland, what my family and kids had to go through?
"He's sitting on TV pretending to wipe a tear from his eye. He deserves an Oscar that fella, making out to be Mother Teresa. People don't know half of it."
Quinn on Keane:
"How do you measure professionalism? By how much pasta you eat? Bleep tests? Abstinence? The ability to get on with it no matter what the circumstances?
"Walking out on your team before the greatest games of their lives?
"We all take responsibility for ourselves. Roy left us in Saipan, not the other way round. And he punished himself more than any of us by not coming back."
But in his autobiography, Quinn's admiration for Keane shone through, even for the way he dismantled McCarthy in front of the Irish squad.
"People talk about Irish patriot Robert Emmet's speech from the dock. They talk about the oratory of Brendan Behan, Eamon de Valera, Michael Collins.
"But Roy Keane's 10-minute oration can be mentioned in the same breath. It was clinical, fierce, earth-shattering to the person on the end of it and it ultimately caused a huge controversy in Irish society."
In August 2002, Keane and Quinn had agreed to shake hands in front of the world when Manchester United visited Sunderland.
But their attempt to make a public reconciliation fell flat when Keane was sent off after being wound-up by Jason McAteer.
Quinn attempted to speak to Keane only to receive the hairdryer treatment from United boss Sir Alex Ferguson, who had misread the situation.
Quinn once said of Keane: "His weakness is his unforgiving attitude to his team-mates. That's where Roy and I will always differ."
But with the hatchet now seemingly buried, the two opposites appear to be an attractive proposition for a club who have suffered a dramatic demise.
Quinn hopes Keane can help him turnaround the club
Keane and Quinn will either prove to be the ideal good cop-bad cop partnership that Sunderland need or a high-stakes gamble with the potential to go spectacularly wrong.
McAteer once admitted that players raise their game for fear of upsetting Keane.
It will certainly offer something for Sunderland's under-performing players to think about in the coming weeks.
If anything, it promises to be an interesting period for all concerned, in particular when Sunderland make the trip to face Mick McCarthy's Wolves side on 25 November.