Brutus was a direct descendant of a man most Romans viewed as a Hero (this Hero was also called Brutus) 400 years before Caesar the first Brutus had assassinated the last Roman tyrant/king and had freed the people of Rome from oppressive rule, this original brutus had then refused to be crowned King and had instead set up the republic of rome giving people their freedom, because he killed a bad guy and then refused to be king and instead gave power to the people, this Brutus was still a hero 400 years later, his descendants (the Brutus clan) tried to live up to their founder's ideals and look after the very poorest people in rome, the Brutus of Caesar's time was the last in the line and was admired by the people of Rome for being fair and kind, and Brutus himself tried to behave like his distant ancestor - hence he killed Caesar not for personal gain but because he believed Caesar was becoming like the guy his ancestor had killed 400 years before and he believed that by killing Caesar he was saving Rome and it's people from a tyrant
