The rulers of Rome included senators such as:
Marcus Brutus, Decimus Junius Brutus Albinus and Gaius Cassius Longinus, who were all powerful men.
All of them together agreed to kill the King of Rome, Julius Caesar.
This was done in response to the growing popularity and power of Julius Caesar which many of these men did not like.
In the aftermath of the assassination, the murderers were spared by the Senate through a compromise which would keep most of Julius Caesar's appointees within the senate.
The lure of power left many mouths shut, which, to modern historians means that the there was a widely accepted conspiracy against the king.