Ronaldo's football abilities were first recognised when he was 14. He was recommended to the Brazil youth team by World Cup winner Jairzinho, who also arranged for his own former club, Cruzeiro Esporte Clube, to sign him when he was old enough for a professional contract.

Ronaldo scored 12 goals in 14 games in the Brazilian National Championship, and in the Minas Gerais State Championship he scored all three goals in Cruzeiro's 3-1 victory against arch-rival Atlético Mineiro.

He was soon transferred for US$6 million to PSV Eindhoven and later attracted the attention of Spain's FC Barcelona. He played for Barça in the 1996-97 season, scoring 34 goals in 37 appearances (47 in 49, including appearances in the Copa del Rey and European Cup Winners Cup), and then transferred to Inter Milan the following year. A year after the 1998 FIFA World Cup, he severely injured his right knee and was out of the game for several months. During his first comeback in 2000, he played only seven minutes during a league game against Lazio before injuring his knee for a second time. After two operations and 20 months of rehabilitation, Ronaldo came back for the 2002 FIFA World Cup, in which he scored two goals against Germany in the final. Ronaldo was the top scorer of the 2002 World Cup with nine goals, helping Brazil win their fifth World Cup title.

Later in 2002 he won the World Player of the Year award for the third time, and transferred from Inter to Real Madrid for approximately €39,000,000, after frequent disputes with Inter coach Héctor Cúper

His transfer to Madrid was the subject of a media frenzy not just laced with the usual hype because of his reputation, but more so because he was now the third successive Galactico (or superstar) signed in as many years by the Spanish giants as part of their policy of signing the world's biggest superstar football players in order to maintain their levels of success whilst broadening their reaches of fame.[citation needed] Ronaldo was such a well-known signing that sales of his shirt on the day of his signing alone broke all records the world over

Proof of his fame came with the fact that even though Ronaldo was sidelined through injury until October 2002, fans continued to chant his name in the stands. Ronaldo scored twice in his debut for Real Madrid.

That same reception was observed on the night of the final game of the season against Athletic Bilbao, where Ronaldo scored again to seal his first season with 23 league goals (not including the goals in the UEFA Champions League that included a hat-trick away at Manchester United - which the Manchester United fans gave him a standing ovation for, as he was substituted, which showed great respect for Ronaldo's ability) and the La Liga Championship title for 2003, which Ronaldo had previously failed to win whilst at FC Barcelona. Recently, in May 2006, Ronaldo and teammate Antonio Cassano were fined for every gram that they remained overweight.

After the World Cup in Germany, there was speculation that Ronaldo would leave Real for A.C. Milan in a trade for Kaka. Ronaldo had previously threatened to leave the club after repeated jeering from supporters about his weight and he was expected to face competition from new signing Ruud van Nistelrooy. Milan later ended negotiations with Real. He has also been linked with a swap deal for Inter Milan's Adriano, although no official bid has been made.[4] Ronaldo scored his first goal of the season in La Liga on 3rd December 2006, Although rumours are still abound that Ronaldo could be out of Real Madrid and moving to AC Milan.