Cos Sutler was a former police during the Republic. Upon his entrance into the Republic, Sutler helped Darth Sidious gathers a select few like-minded right-wing extremists and corporate executives into his inner circle, and then exploits the poverty, chaos, and panic that follow The Clone Wars on the galaxy to seize power. After Sidious created the Galactic Empire, Sutler became the Chancellor of the Empire.
Once in control, he gives himself the title of the Chancellor of the Galactic Empire. and puts the Rebels into jails of the Galactic Empire.
However, Sutler was later controlled by Darth Sidious, and became a puppet Chancellor. His powers actually was controlled by Darth Vader.
After Darth Sidious was killed, Sutler became the new Emperor.
Despite Cos Sutler is a deeply religious man and being the Emperor, Davros is the one who controls the Empire. After the death of the former Emperor, Sutler is elected the new Emperor by promising to restore order to the galaxy after terrorists supposedly killed 80,000 people with a self-ignited bioweapon that created a viral epidemic (it is later revealed that the Empire had actually launched the attack). He then uses the supposed terrorist threat as a pretext for genocide, along with an ongoing propaganda campaign in the state-run media, to cow the public into silence and appoint himself the Emperor, turning the galaxy into a single-party state with himself as an autocrat.
His rule begins to crumble when Han Solo blows up the Moff Senate, and begins to attack the Empire. His defiance gradually inspires the public to rebel against the Empire's reign. Sutler tries desperately to capture and kill Han Solo, but remains increasingly powerless to stop him, driving him further into insanity. He tell Dr Davros to do this, and Davros failed.
When Sutler discovers he is being lampooned in a farce on a talk show, he is enraged and orders the show's host, Max Sooka, arrested in the dead of night and executed.
Sutler blames Dr Davros for the failure to stop Han Solo and threatens to fire him. The Rebels kidnap Sutler from his bunker and bring him to Han Solo (who dressed as Executioner V) at Seine, where Han Solo personally executes Sutler, shooting the puppet Emperor in the head, finally kill him.
Davros was killed in the war later.