Ronald Antonio "Ronnie" O'Sullivan (born 5 December 1975) is an English professional snooker player known for his rapid playing style, and is nicknamed "The Rocket". He has been World Champion on four occasions (2001, 2004, 2008 and 2012) and, with career earnings of over £6 million is second after Stephen Hendry on snooker's all-time prize-money list. O'Sullivan has been the world's no. 1 player on five occasions, and has won a total of 24 ranking titles. He is second, again behind Hendry, on the list of players making the most competitive century breaks, with a total of 678. O'Sullivan has compiled 11 maximum breaks in professional competition, a record which he shares with Hendry. He also holds the record for the fastest maximum break, at 5 minutes 20 seconds.

O'Sullivan is considered by many fans, critics and professionals, including fellow multiple-World Championship winners Hendry and Steve Davis, as the most naturally talented player in the history of the game. He has, however, been involved in a number of controversial incidents during his career.