Brutus was the adopted son of Julius Caesar. However he participated in the collective murder of the dictator, and then went on to try to take power in the Roman Empire. In the end, he lost to Caesar's heir, Octavius.
This story is told in William Shakespeare's play, Julius Caesar, where Brutus is effectively the tragic hero of the play - he admires Caesar, yet kills him because he would rather save Rome than his friend. However, due to idealistic rather than efficient management of the situation, an empire is finally set up in Rome.