London - When Arsenal face Manchester United in a crucial Premier League clash on Saturday, the antics of the two sworn enemies on the touchline will take up as much attention as the actual match.
It was ever thus when Arsenal boss Arsene Wenger and United manager Jose Mourinho lock horns.
The acrimony between Wenger and Mourinho stretches back to the arrival of the Portuguese coach in England 13 years ago.
Verbal volleys have been traded time and again, with the enmity once boiling over into a memorable mid-match bout of shoving.
Even now, with Wenger 68, and Mourinho 54, neither boss seems ready to act their age.
Why do the old foes hate each other so much? Here AFP Sports looks back at the roots of the rivalry and recalls some of their more spectacular battles:
Wenger labelled a "voyeur"
When Mourinho joined Chelsea in 2004, his brash personality didn't take long to ruffle Wenger, who as one of the game's established force, didn't take kindly to being threatened by the young upstart.
While Mourinho adopted a deferential attitude around Manchester United boss Alex Ferguson, there would be no such respect shown to Wenger.
When Wenger took a shot at Chelsea by claiming they might have lost belief after a couple of poor results in 2005-06 season, Mourinho went on the offensive with a memorable, if unkind, description of the Arsenal manager.
"I think he is one of these people who is a voyeur. He likes to watch other people," he said.
"There are some guys who, when they are at home, they have a big telescope to see what happens in other families. He speaks and speaks and speaks about Chelsea."
The saying goes that opposites attract, but the contrast between the urbane Wenger and the spiky Mourinho couldn't be more obvious and neither has been willing to end the cold war.
The differences between the rivals' approach to their careers are striking.
Former Real Madrid, Inter Milan and Porto coach Mourinho has never lasted more than three years anywhere, while Wenger is in the 21st year of his Arsenal reign.
Wenger took a holistic approach to his root and branch rebuild of Arsenal and has produced some of the most eye-catching teams in English football history, but when results suffered his stubborn refusal to tinker with his purist principles was costly.
Mourinho prefers to shock and awe, hammering away at perceived threats both inside and outside his clubs until they bend to his will -- the results have been remarkable but on occasions his acerbic tongue has proved his downfall when players start to tune him out.
"Specialist in failure"
Three words delivered in typically witheringly fashion by Mourinho struck at the heart of Wenger's weakness in February 2014.
Arsenal had gone eight years without a trophy under Wenger at the point, while Mourinho was back at Chelsea having hoovered up silverware across the world.
In a pointed jibe at Mourinho, the Gunners chief claimed Premier League bosses were playing down their title chances because they "fear to fail".
Mourinho came back with all guns blazing, saying: "He is a specialist in failure, I'm not.
"The reality is he's a specialist because, eight years without a piece of silverware, that's failure. If I did that in Chelsea I'd leave London and not come back."
PUSH COMES TO SHOVE
Furious after Chelsea defender Gary Cahill's ugly tackle on Arsenal's Alexis Sanchez in the first half of a spiteful London derby, Wenger came out of his technical area to remonstrate with referee Martin Atkinson.
Mourinho didn't miss the chance to have his say and Wenger responded with a shove in the chest of his rival, who stumbled before regaining his balance and pointing to tell the Frenchman to get back to the bench.
The pair clashed again seconds later with the fourth official Jonathan Moss stepping in to separate them.
With Chelsea winning the October 2014 meeting 2-0 to inflict the Gunners' first league defeat of the season, it was no surprise there was no handshake between the bosses at full-time.