He overthrew the Tarquin monarchy in 509 BC.

Lucius Junius Brutus, was a friend of Lucretia's family, and he took both the knife and Lucretia's body to the Forum, where he used them to enrage the people into rebellion. Tarquin was out of town when this happened; he tried to return, only to find himself locked out, and the whole army turned against him. The only thing he could do was go into exile, so he departed for the Etruscan city of Clusium. On that note the Roman monarchy ended in 509 B.C., and in its place came the Roman Republic, with Brutus as one of its first consuls. What a way to overthrow someone..lol
Coup

Absolutely correct! Thanks for your answer, Sagus!