#5 Denis Irwin
Irwin was one of Ferguson’s earliest signings and also one of his best. This Irish left-back was one of the reasons behind United’s rise to becoming one of the leading football clubs in the world.
He spent 12 years at United and collected 7 Premier League trophies and a Champions League title. Ferguson signed him from Oldham Athletic in 1990 and throughout the 90s, Irwin contributed immensely toward United’s rise.
Irwin made very few mistakes defensively, made overlapping runs quite often and performed well in big matches. All those qualities made him an indispensable member of the side and nobody has been able to properly replace him at United since he left in 2002, though Patrice Evra, another great player recruited by Sir Alex, came close.