Former Barca midfielder Josep "Pep" Guardiola, 40, took over as coach in June 2008, leading the club to an unprecedented treble of Spanish league and cup and European Champions League in his first season in charge.
His lavishly-praised side, who overcame Sir Alex Ferguson's United 2-0 in the final of Europe's elite club competition in 2009, have gone on to win two more Spanish league titles, as well as the European Super Cup and the Club World Cup.
Ferguson moved on from a playing and coaching career in his native Scotland to managing United in 1986 and, since claiming the FA Cup a barren four years later, the 69-year-old has won more than 30 trophies, including 12 domestic league titles, four more FA Cups and two Champions Leagues.
Ferguson's success and the strength of his personality have helped him to forge a seemingly unassailable position at the English Premier League club and he has defied his critics and the march of time to remain at the helm while many others have fallen by the wayside.
He has done so while often risking the wrath of the fans, releasing crowd favourites such as Paul Ince and David Beckham when he felt the time was right as, during his remarkable 25-year stint, he has overseen the rebuilding process from one great team to another with barely a dip in between.
Guardiola earned his status as a Barcelona club hero while still a player and his performance as coach has put him in an unusually stable position in a country where clubs hire and fire with alarming regularity.
"Alex Ferguson has won absolutely everything. He lives for his club and he is an example for other coaches," Shakhtar Donetsk boss Mircea Lucescu said on UEFA.com this week.
"The same goes for Josep Guardiola," the Romanian added. "He grew up in Barcelona and he spent most of his life with the club, so he shares their philosophy.
"You can hardly imagine either coach going off to sign for someone else."
KILLER BLOW
As a product of Barca's youth system, Guardiola has played and coached only one basic style: keep possession, make the other team chase the ball and carve open defences with a swift interchange of short passes or a perfectly weighted assist.
Ferguson, by contrast, tends to field more muscular teams, with tall, burly centre backs and combative midfielders feeding pacy forwards who can destroy opponents with devastating counter-attacks.
In the 2009 final, United rocked Barca in the early stages with their harrying and chasing and Samuel Eto'o's opening goal in the 10th minute was against the run of play.
Once Barca get ahead they are masters at holding on to the ball and wearing down opponents before dealing a killer blow, as in Rome when Lionel Messi struck with a header to end United's hopes of a comeback.
"Barcelona's forte is possession, controlling the direction and rhythm of the game; they know exactly what they have to do," Lucescu said.
"United are a better-built team physically, with fast
