If you mean the Brazilian Ronaldo he's famous because he scored a lot of goals and holds the record for most goals scored overall in the World Cup.
If you mean the Portugese Cristiano Ronaldo he's famous because he plays for Man Utd, he's a player with exceptional talent but doesn't always use it right.
Hope that helped.
You should like Kaka , as he is famous and also popular, he never cheats to win free kicks and penalties like Ronaldo does.
When Kaka's brothers were young, they were unable to pernounce Kaka's first name, Ricardo. So, they called him "Caca" instead, and "Caca" eventually turned into "Kaka".
Kaka is popular as he is young, talented, and a fantastic player, he is a family man of high morals, not involved with girls or cheating.
Cristiano Ronaldo, because it is in the 21st Century.
which area is ronaldo famous for