Which ancient Greek philosopher was a decorated champion wrestler whose famous name was actually a nickname meaning 'broad-shouldered'?

Plato

A later tradition says Plato was originally named Aristocles and received the name “Plato,” meaning “broad,” from his wrestling teacher because of his physique; other explanations connected it to his eloquence or forehead. Some ancient writers also claimed that he wrestled at the Isthmian Games, but calling him a decorated champion overstates the surviving evidence.