Thiago Machado Vilela Pereira (born 26 January 1986) is a retired Brazilian international competition swimmer. One of the greatest swimmers in the history of Brazil, Pereira won the silver medal in the 400-meter individual medley at the 2012 Summer Olympics in London, beating the then-current Olympic champion Michael Phelps. He also broke a world record in the short course 200-meter individual medley, and broke several South American and Brazilian records. During his career, he competed with swimming legends Michael Phelps and Ryan Lochte.
Pereira is a resident of Belo Horizonte, and became known as Ricardo Prado's successor in his native country after winning the silver medal in the 200-meter individual medley at the Pan American Games in Santo Domingo, Dominican Republic in 2003. In 2004, he won the world title in the same event at the 2004 FINA Short Course World Championships. After that, Pereira won six gold medals at the 2007 Pan American Games in Rio de Janeiro, breaking the record of five gold medals won in one Pan American Games, previously held by Mark Spitz. Pereira broke the short course 200-meter individual medley world record later that same year. He represented Brazil at three consecutive Summer Olympics, starting in 2004.
As of July 2015, Pereira is the Brazilian athlete with most gold medals won in Pan American Games: 15 earned in four Pan American Games. In 2015, Pereira became the athlete with the most medals in the history of Pan American Games, surpassing the Cuban gymnast Eric López, who won 22 medals between 1991 and 2003. Pereira finished Toronto with 23 total medals.