While modern depictions make Brutus out to be Caesar's BFF and biggest betrayer, he wasn't really the Judas of the group that planned his assassination. That would be Decimus. Brutus was the son of his mistress. He had previously sided with Caesar’s enemy Pompey in the Roman Civil War but returned to Caesar's side after the conflict because he was given prominent political positions. Decimus was one of Caesar's trusted, loyal friends and convinced him to leave his house on the Ides of March.