#3 Roy Keane
Legendary midfielder Roy Keane is third on our list of the greatest signings made by Sir Alex Ferguson at Manchester United. The Irishman joined Manchester United from Nottingham Forest back in 1993 in a deal worth €8.50 million, a British record transfer fee back in the day.
Keane soon grew into an influential figure at the club and was appointed captain by Sir Alex Ferguson. His greatest achievement as captain was leading the club to a historic treble in the 1998-99 season, albeit missing the final against Bayern Munich.
Before leaving the club in 2006 for Celtic following a feud with Sir Alex, Keane made 471 appearances, the fourth-highest in the club's history. He won seven Premier League titles, a Champions League and four FA Cups in his 13-year stint with Manchester United.
#2 Cristiano Ronaldo
One of the greatest players of all time, Cristiano Ronaldo's talent was first identified by Sir Alex Ferguson when the Portuguese was still a wiry winger playing for Sporting Lisbon. Manchester United signed Ronaldo in 2003 for a fee of €19 million, and he spent the next six years with the club, winning everything there is to win in English football.
Ronaldo played 292 matches under Sir Alex Ferguson, scoring 119 goals in his first stint with Manchester United. He won three Premier League titles, a Champions League, an FA Cup and two League Cups during that time. He also won the Ballon d'Or in 2008 for leading the club to the Champions League title that season.
Though Ronaldo grew into a goal-scoring behemoth at Real Madrid, it was at Manchester United and under Sir Alex's tutelage that the world first took note of him. He has now returned to the club for a second stint, joining the side on a two-year deal from Juventus earlier this summer.
#1 Eric Cantona
The greatest signing made by Sir Alex Ferguson at Manchester United has to be Eric Cantona. Cantona joined United in 1992, six years into Sir Alex's association with the club, during which Manchester United won just one League Cup. But his signing changed everything.
Manchester United won the league title in all but one of Cantona's five seasons with the club. United won two FA Cups during that time too. In all, the legendary forward scored 81 goals and provided 62 assists in 180 appearances for the club.
Sir Alex penned a heartfelt letter to the Frenchman when he abruptly decided to bring an end to his career shortly after winning the 1996-97 Premier League.