César Augusto Cielo Filho (born January 10, 1987 in Santa Bárbara d'Oeste, São Paulo, Brazil) is a Brazilian professional swimmer who specializes in sprint events. He is the most successful Brazilian swimmer in history, having obtained two Olympic medals, four World Championships gold medals and breaking a world record within a one-year span.

Cielo is the current world record holder in the 100 meter and 50 meter freestyle. His gold medal at the 2008 Summer Olympics, in the 50 meter freestyle competition, is Brazil's sole Olympic gold in swimming to date.

Cielo began his career at small swimming clubs in his native state. As a young teenager, Cielo trained at the Esporte Clube Barbarense under coach Mario Francisco Sobrinho. When he was 13, Cielo started training in Piracicaba at the Clube de Campo de Piracicaba under coach Reinaldo Rosa. At the age of 16, he transferred to Esporte Clube Pinheiros, in São Paulo, to train and develop with coach Alberto Silva and Brazilian swimming legend Gustavo Borges. In 2005, he received a scholarship from Auburn University, in the United States, where he trains under Australian coach Brett Hawke. Cielo competed for eight-time NCAA National Champion Auburn Tigers' Swimming and Diving team. He was also tutored by short-distance specialist Fernando Scherer in 2008.

Michael Fred Phelps (born June 30, 1985) is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions. In doing so he has twice equaled the record eight medals of any type at a single Olympics achieved by Soviet gymnast Alexander Dityatin at the 1980 Moscow Summer Games. His five gold medals in individual events tied the single Games record set by compatriot Eric Heiden in the 1980 Winter Olympics and equaled by Vitaly Scherbo at the 1992 Summer Games. Phelps holds the record for the most gold medals won in a single Olympics; his eight at the 2008 Beijing Games surpassed American swimmer Mark Spitz's seven-gold performance at Munich in 1972. Phelps' Olympic medal total is second only to the 18 Soviet gymnast Larisa Latynina won over three Olympics, including nine gold. Phelps also holds the all-time record for most gold Olympic medals, at 14.