Ronaldo was born in Santo António, a neighbourhood of Funchal, Madeira, the youngest child of Maria Dolores dos Santos Aveiro, a cook, and José Dinis Aveiro, a municipal gardener.[3] His second given name, "Ronaldo", was chosen after then-U.S. president Ronald Reagan, who was his father's favourite actor.[4][5] He has one older brother, Hugo, and two older sisters, Elma and Liliana Cátia.[1] His great-grandmother Isabel da Piedade was from Cape Verde.[6] The family was staunchly Catholic. Ronaldo later said that he grew up in poverty, sharing a room with his brother and sisters.[7]

As a child, Ronaldo played for amateur team Andorinha, where his father was the kit man,[8] and later spent two years with local club Nacional. In 1997, aged 12, he went on a three-day trial with Sporting CP, who signed him for a fee of £1,500.[9][10] He subsequently moved to Alcochete, near Lisbon, to join Sporting's other youth players at the club's football academy.[9] By age 14, Ronaldo believed he had the ability to play semi-professionally, and agreed with his mother to cease his education in order to focus entirely on football.[11] While popular with other students at school, he had been expelled after throwing a chair at his teacher, who he said had "disrespected" him.[11] A year later, however, he was diagnosed with a racing heart, a condition that could have forced him to give up playing football.[12] He underwent an operation in which a laser was used to cauterise the affected area of his heart; discharged from hospital hours after the procedure, he resumed training only a few days later.[13]