Manchester - As Arsene Wenger and Rafael Benitez will testify, Jose Mourinho has had more than his fair share of public confrontations with opposing managers during his career.
None of them, though, have been as bitter or keenly-felt as Portuguese Mourinho's long-running rivalry with Spaniard Pep Guardiola. Manchester, the most passionate of football cities, is about to get very lively indeed.
As United's new manager, Mourinho will have his City counterpart Guardiola as a football neighbour next season.
It is perhaps just as well that the clubs no longer have adjoining training grounds at Carrington, with City having moved across Manchester to a purpose-built base near the Etihad Stadium two years ago. Mourinho and Guardiola will not be on each other's doorsteps, but they will be close enough.
"The grudge match arrives in Manchester" was the headline in Madrid-based newspaper Marca on Monday, although it will arrive first in Beijing, where City and United will meet in an International Champions Cup pre-season game on July 25.
The grudge dates back to 2008, when Mourinho was overlooked for the Barcelona manager's job in favour of the inexperienced Guardiola, who was promoted from coaching the club's B team.
The gamble paid off for Barcelona, who won the treble of Champions League, La Liga and Copa Del Rey the following season, making Guardiola's name as a coach.
Mourinho went instead to Inter Milan and, en route to winning the 2010 Champions League title, took great delight in defeating Guardiola's team in the semi-finals, to the extent that he was involved in a confrontation with Barcelona goalkeeper Victor Valdes at full-time.
It was when Mourinho replaced Manuel Pellegrini at Real Madrid that summer that the rivalry became toxic.
Guardiola, in the face of regular goading from his rival, snapped during a run of four 'El Clasico' meetings in three weeks, criticising Mourinho's capacity for public theatrics and sarcastically calling him "the chief, the f***ing man".
That outburst came ahead of another two-legged Champions League semi-final meeting between the two managers, which Guardiola won this time, going on to lift the trophy.
Arguably the most notorious flashpoint, though, came when Real and Barcelona met in the 2011 Spanish Super Cup. As the match descended into a brawl, Mourinho was captured on camera gouging the right eye of Tito Vilanova, Guardiola's assistant.
The two managers have wildly contrasting public personas, and different approaches to the game; Guardiola does not enjoy the confrontations on which Mourinho thrives; the new City manager is an exponent of stylish football, while his United counterpart sees himself first and foremost as a winner.
Yet they share more than a status as arguably the two most sought-after managers in world football; they worked together for four years at Barcelona from 1996, where Guardiola was a player when Mourinho arrived as assistant to the late Bobby Robson.
After Robson moved on, Mourinho stayed on to assist Louis van Gaal, the man he is now replacing at Old Trafford, and regularly took training sessions as he developed his coaching skills.
Mourinho and Guardiola arrive in Manchester with a shared past, pressure to succeed and significant budgets to help them.
Their contests will be significantly louder than the ones seen over the last two years between the softly-spoken Pellegrini and the embattled Van Gaal. Even Alex Ferguson's rivalries with his City counterparts never reached such levels.
Then again, City had 14 permanent managers and four caretakers during Ferguson's 26-and-a-half years at Old Trafford, so there was rarely time to build a rivalry.
Ferguson did refer to the 'noisy neighbours' as City began to catch up with them in the wake of Sheikh Mansour's 2008 takeover at Eastlands. The noise from both halves of the city has just been turned up to maximum.
Meanwhile, Swedish star Zlatan Ibrahimovic, linked with a possible move to United after leaving Paris Saint-Germain, on Thursday praised Mourinho, his coach at Inter Milan from 2006 to 2009.
"I think it's a great move," for Manchester United to hire Mourinho, he said. "You want action, you bring Mourinho. I believe he's the man to bring them back to the top. Wherever he went he won."