Julius Caesar was killed by members of the Senate. Though it is believed that up to 60 people may have been involved in the assassination, the exact number is unknown. It is equally impossible to know who struck the fatal blow.
Rome was a well-established Republic by the time Julius Caesar came to power. Though Roman law allowed the Senate to relinquish power to a dictator in times of need, the action had historically only been done for short periods of time and only when the need to do so was extreme. When Julius Caesar became "dictator for life" in 44 B.C., the Senate felt threatened. The members felt that Caesar was attempting to usurp too much power and was now a threat to the Republic. The members of the Senate also felt their own status within society was threatened by those favored members of Caesar's military. These factors caused them to begin plotting Caesar's assassination.
One of the most shocking aspects of the plot was the involvement of Marcus Brutus, Caesar's protégé, whose life Caesar had recently spared following defeat in battle. Some accounts of March 15, 44 B.C., the day Caesar was killed, claim Caesar was handed a note warning him of the plot as he entered the Senate, though this has never been substantiated. When he entered, he was surrounded and stabbed repeatedly.