#2 Sir Alex Ferguson (Manchester United)
The legacy of Sir Alex has only been magnified by the mess that has come after him. Since the great man stepped aside in 2013, the Red Devils have gone through three managers (David Moyes, Louis Van Gaal, and Mourinho), spent in excess of £750m since on transfers but are yet to win a Premier League title since.
The Scotsman had done a magnificent job at Aberdeen, knocking Glasgow giants; Celtic and Rangers off their perch to win the Scottish League. He had followed it up with an unprecedented European Cup Winners Cup triumph in 1983.
Manchester United had been in a slump before Fergie arrived with bitter Northern rivals, Liverpool the dominant British side. United had become an also-ran after the departure of the great Sir Matt Busby and had not won the league in 19 years before Sir Alex showed up.
He changed the mentality, philosophy, and status of the club dramatically during his 26 years in charge. His astute use of academy prospects, unheralded foreign signings and experienced players to good effect.
The style of play he fostered; constant attacking with two wingers ably supported by a strong backline has become known now as the "United Way". This emphasis on attacking, entertaining football brought unprecedented success to the Red Devils.
The 38 trophies won under Ferguson's reign represent Manchester United's greatest-ever era of success. It is one that may never be topped in the history of the club.