I'm assuming you mean after the defeat of Brutus and Cassius also, in which case is was Octavian Caesar (JC's great-nephew and adopted heir), Marc Antony, and Lepidus.

Lepidus was by far the politically weakest member of this group.  As the play chronicles, Antony was ready to get rid of him almost immediately after winning.  He was originally included in the triumvirate almost soley because he commanded a large army and had loads of money.   Lepidus lost his power when most of his armies deserted him in favor of Octavious.

Marc Antony suffered from a bitter bout of jealous after not receiving a large portion of Caesar's will.  Antony was angry about not receiving more power than Octavius, and eventually started a battle to earn that power.  Antony's army was defeated five years after Lepidus was removed, leaving OC as the sole remaining leader.  Antony, of course, committed suicide with Cleopatra.

Octavius was destined for greatness when he was named heir to Julius Caesar.  Following the events of the play, he would become the first emporer of Rome, not quite what JC had imagined but close enough.  After defeating Antony's army, OC united and organized provinces in Egypt, Syria, Judea, and Asia before returning home to Rome and being named Augustus Caesar.  This is the Caesar Augustus that we all know from the bible who called for the census that brought Joseph and Mary to Bethlehem.