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Sky Sports' Transfer Show picked the Portuguese superstar's £12 million move to Old Trafford ahead of a host of footballing legends.
Ronaldo was 18-years-old when he joined United and considered an incredibly raw talent.
But he'd go on to fulfill his potential, winning three Premier League titles and the Champions League before joining Real Madrid for £80 million in 2009.
Check out the entire top 20 below.
20. Petr Cech (Rennes to Chelsea)
19. Sergio Aguero (Atletico Madrid to Manchester City)
18. Eden Hazard (Lille to Chelsea)
17. Patrick Vieira (AC Milan to Arsenal)
16. David Silva (Valencia to Manchester City)
15. Gianfranco Zola (Parma to Chelsea)
14. Virgil van Dijk (Southampton to Liverpool)
13. Dennis Bergkamp (Inter Milan to Arsenal)
12. N'Golo Kante (Caen to Leicester City)
11. Mohamed Salah (Roma to Liverpool)
10. Alan Shearer (Blackburn to Newcastle United)
9. Vincent Kompany (Hamburg to Manchester City)
8. Wayne Rooney (Everton to Manchester United)
7. Sol Campbell (Tottenham Hotspur to Arsenal)
6. Didier Drogba (Marseille to Chelsea)
5. Roy Keane (Nottingham Forest to Manchester United)
4. Frank Lampard (West Ham to Chelsea)
3. Eric Cantona (Leeds to Manchester United)
2. Thierry Henry (Juventus to Arsenal)
1. Cristiano Ronaldo (Sporting CP to Manchester United)
Ronaldo has gone on to prove the doubters wrong regarding his career and is now playing for Italian giants Juventus.
Sky Sports' Tom White revealed: "When he signed I thought he was a poor signing for United.
"So from now on, don't listen to a word I say."
While Ronaldo came out on top in the poll, he did spend less time in English football than second placed Thierry Henry.
Henry joined Arsenal in 1999 and became the focal point of Arsene Wenger's side.
An unbeaten season in 2003/2004 birthed the 'Invincibles' moniker and Henry was their main attacking outlet.
"We wondered who this player was [when Arsenal signed him]," Jim White explained. "Well we soon found out. Henry for Arsenal - an absolute standout Premier League player."
Current Premier League champions Liverpool have two of their current players on the list in the form of Mohamed Salah and Virgil van Dijk.
Who do you think is the Premier League's best ever signing?
Featured Image Credit: PA Images
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