Ronaldo was born in Funchal in the Madeira Islands where he started his career at Nacional before moving to Sporting Lisbon.
He made his debut for Sporting in the Portuguese Super Liga in September 2002 at the age of just seventeen.
Cristiano caught the attention of many - United players included - during the pre-season friendly which marked the opening of Sporting's new stadium, a game in which Ronaldo scored. The Reds management had been watching him for some time, however.
"After we played Sporting last week the lads in the dressing room talked about him constantly, and on the plane back from the game they urged me to sign him. That's how highly they rated him," revealed Sir Alex Ferguson at his signing press conference.
"It was only through our association with Sporting that they honored our agreement of months ago," Ferguson said.
""He is one of the most exciting young players I've ever seen, an extremely talented footballer. He's a two-footed attacker who can play anywhere up front: right, left or through the middle," he concluded.
Cristiano, who appeared 25 times for Sporting last season and scored three goals, added: "I am very happy to be signing for the best team in the world, and especially proud to be the first Portuguese player to join Manchester United.
"I look forward to helping the team achieve even more success in the years to come."