Marcus Junius Brutus was a character in Shakespeare's play Julius Caesar (based on a historical figure), set in the waning days of the Roman Republic. He was the best friend of the play's namesake, but ultimately plotted to kill Caesar. On the Ides of March, he stabbed his friend in the back.
Elim Garak once claimed that he would have been most, rather than least, suspicious of Brutus had he been in Caesar's place, but according to Doctor Bashir Caesar's inability to suspect treason from Brutus was what made it a tragedy. (TOS: "The Conscience of the King"; DS9: "Improbable Cause")