Gaius Cassius Longinus, was a Roman senator, a leading instigator of the plot to kill Julius Caesar, and the brother in-law of Marcus Junius Brutus, he commanded troops with Brutus during the Battle of Philippi against the combined forces of which Roman politician and general who played a critical role in the transformation of the Roman Republic from an oligarchy into the autocratic Roman Empire?
Gaius Cassius Longinus:  He commanded troops with Brutus during the Battle of Philippi against the combined forces of Mark Antony and Octavian, Caesar's former supporters, and committed suicide after being defeated by Mark Antony. Mark Antony: Marcus Antonius (Latin: ; January 14, 83 BC – August 1, 30 BC), commonly known in English as Mark or Marc Antony, was a Roman politician and general who played a critical role in the transformation of the Roman Republic from an oligarchy into the autocratic Roman Empire.
Mark Antony