Regicide is an achievement/trophy in Dishonored.
How to Acquire
For this achievement, Corvo Attano must assassinate the Lord Regent, Hiram Burrows, during the mission Return to the Tower.
In low chaos the Lord Regent will be in his room, unless an alarm within Dunwall Tower has been triggered. If this happens, Corvo will need to kill him in his safehouse on the roof.
In high chaos the Lord Regent will always be in his safehouse on the roof.