Davros

An Emperor Dalek was usurped by Davros, who refered to him as "the upstart". (COMIC: Nemesis of the Daleks, Emperor of the Daleks!)

Civil War
After Davros was captured by the Daleks on Necros, the Emperor personally attended his trial on Skaro. The Emperor charged Davros with perverting the destiny of the Daleks, while Davros protested that the Emperor had allowed the Daleks to become weak. Though a number of Daleks considered that they could learn from Davros, the Emperor sentenced him to extermination. Before the sentence could be carried out, the Dalek City was struck by an asteroid while the Daleks' systems were incapcitated by a virus. In the ensuing chaos, Davros was escorted by technobots to the Sixth Doctor and Peri Brown, who took him with them in the TARDIS. From the court room, the Emperor presented video evidence of Davros consorting with the Doctor.

To exact revenge on both of them, the Emperor had Dalek Killer Abslom Daak transmated just before he would have died destroying the Death Wheel in orbit of the planet Hell. Using androids as a decoy, the Emperor secretly gave Daak the task of capturing the Doctor, ostensibly to aid humanity's effort against the Daleks. Once Daak and the Star Tigers captured the Seventh Doctor and Bernice Summerfield on Hell, they were transmated to Skaro, where the Emperor revealed himself. Though an attempt at escape was made, the Daleks quickly pacified the humanoids. Under interrogation, the Doctor was forced to reveal to the Emperor that he had taken Davros to Spiridon, while his friends were conditioned to serve the Daleks and used to force the Doctor to assist the Daleks in eliminating him. While the Emperor remained on Skaro, the Doctor and his friends accompanied an Dalek fleet led by the Black Dalek to Spiridon, where they engaged Davros' Daleks in battle. Ultimately, Davros' Daleks prevailed over those loyal to the Emperor, while the Doctor was able to set his allies free.

Naming himself the new Emperor of the Daleks, Davros took the Doctor and his company with him aboard his mothership, which set a course to Skaro. Upon arrival, the mothership transmitted a computer virus to impair the Dalek City's systems before launching an attack, soon reducing it to ruins. Touching down in his assault shuttle, Davros proceeded to confront the Emperor. A brief argument ensued, after which Davros deemed that the Emperor was no longer needed and ordered his extermination. Subjected to the firepower of two of Davros' Daleks, the Emperor was was seemingly killed as his casing was blown apart.

Shortly following the Emperor's death, the Doctor and his allies escaped, though not before Davros was badly wounded by Daak. Davros survived this injury, however, and was transfered from his chair to an Emperor Dalek casing. As Davros secured his rule over Skaro, the former Imperial Daleks whom followed the late Emperor became the Renegade Daleks while Davros' Daleks became the new Imperial Daleks, beginning the Imperial-Renegade Dalek Civil War. (COMIC: Emperor of the Daleks!)

However, by a later point in the War, the Dalek Prime, Emperor of the Renegades, had regained control of Skaro. He displayed the ability, during his public confrontation with Davros as witnessed by the Eighth Doctor, to be active in the world through remotely-controlled decoy casings, which could be destroyed at no risk to the real Dalek Prime. (PROSE: War of the Daleks)

Behind the scenes

 * The design of the Dalek Emperor's casing was a combination of Davros' Imperial Emperor casing from Remembrance of the Daleks and the Golden Emperor from The Dalek Chronicles.