Dalek Emperor

The Dalek Emperor was the supreme ruler of the Dalek Empire, commanding the Dalek race and the planet Skaro.

At least six different Emperor Daleks (a.k.a. Dalek Emperor) are believed to have existed, counting Davros.

Dalek Prime
One of the first Daleks, who exterminated Davros and proclaimed the Daleks' future victory over the universe (DW: Genesis of the Daleks), assumed the role of Dalek Prime (later Emperor) and would continue to act as the Emperor throughout Dalek history. (EDA: War of the Daleks)

The Golden Emperor
After the neutronic war that devastated Skaro, the mutants had survived in the casings. The only humanoid Dalek survivors of the war, Yarvelling and the warlord Zolfian encountered a Dalek which persuaded them to build more Dalek casings for their mutated descendants. Before the last two humanoid Daleks died, a special casing was built for the Emperor to reflect its new rank, made of Flidor gold, quartz and Arkellis flower sap. The Golden Emperor was slightly shorter than the other Daleks, with a ridiculously large spheroid head section and in gold rather than grey. It also had three globes on each panel unlike other daleks. (TV21: Genesis of Evil)

The Emperor within the Dalek City
The next known incarnation of the Emperor remained in an enormous, immobile, conical shell plugged into a corner of the control room in the Dalek City on Skaro. It was connected to the wall by tubes. It spoke in an echoing voice.

This Emperor was seemingly destroyed by a civil war between humanised Daleks and un-altered Daleks. However, a light was seen blinking on its casing at the end, indicating some kind of activity. (DW: The Evil of the Daleks)

Davros as Emperor
Davros was made the Emperor of the Imperial Dalek faction of the Daleks. He was encased in a customised Dalek casing with a dome top which could open and close, his body below his head and shoulders covered in a mass of tubing and cables, implying he had greatly deteriorated physically. He was last seen heading for an escape pod just before his ship was destroyed in the wake of the supernova (set off by the Hand of Omega) that consumed Skaro. (DW: Remembrance of the Daleks) Later, Davros' increasingly unstable mind was obliterated by a totally Dalek personality, that of the Emperor. This new Emperor took command of Davros's Daleks and departed. (BFA: Terror Firma)


 * By the time the Tenth Doctor met Davros after the Last Great Time War, Davros' old personality had regained control. 

Emperor of the Dalek Empire
When the Daleks launched an invasion of the Milky Way from the Seriphia Galaxy, a Dalek Emperor was in command. While it successfully conquered much of the galaxy, its real goal was Project Infinity. It intended to summon Daleks from another reality. When those Daleks turned out to be appalled by genocide, the Emperor was captured by the Earth Alliance (BFDE: "Death to the Daleks!", Project Infinity) but transmitted its consciousness into a human, Susan Mendes, to continue the war. (BFDE: Dalek War: Chapter One) It erased her consciousness and intended to use her form to con the galaxy into lowering its guard; however, a psychic trap caused the remnants of Mendes to awaken and trigger the destruction of all Dalek technology, killing the Emperor and devastating the Empire. (BFDE: Dalek War: Chapter Four)

Emperors during the Last Great Time War
It appears two Emperors existed during the Time War. One resided in Kaalann on Skaro. When Skaro was devastated, he was destroyed and the Daleks fled the planet. (VG: City of the Daleks) However, another Emperor came to power and led the Dalek battle fleet in their final attack on Gallifrey. He was believed destroyed at the end of the war. (DW: The Parting of the Ways) During the war, one of these Dalek Emperors faced the Master and took control of the Cruciform (DW: The Sound of Drums) and one formed the Cult of Skaro, a group above and beyond the Emperor, to "think as the enemy thinks" and "imagine" new ways to find victory. (DW: Doomsday)

Unknown to anyone, the Emperor's ship had barely survived the war, falling through time. Afterwards, it went into seclusion and went on to rebuild a new race of Daleks. This Emperor was a Dalek mutant floating in a transparent tank of liquid, topped by a giant-sized Dalek dome, complete with eyestalk, flanked by panels of armour dotted by Dalek "bumps" with a ring-shaped "throne" on the bottom. Because this Emperor had recreated the Dalek race, it saw itself as a god. It had transformed its Daleks from fascists to religious fanatics worshipping it. The Emperor was apparently atomized along with the rest of the Daleks by Rose after she had absorbed the energies of the time vortex and became the Bad Wolf entity temporal paradox in 200,100. (DW: The Parting of the Ways)

The Progenitor Dalek Emperor
When the New Dalek Paradigm went back to the ruined Skaro, they created a new Emperor Dalek, reusing the shell of the old one, albeit with new paint. His blue colouring suggests he was a Strategist Dalek, had ties to that role or was the mastermind of all of the Daleks' plans for universal conquest. When the Eleventh Doctor and Amy Pond travelled back in time to when Skaro was devastated and before the new Daleks arrived with the Eye of Time, they erased the Daleks' alterations and Kaalann was left abandoned. The new Emperor was never created as a result. (VG: City of the Daleks) When the New Dalek Paradigm took control of Earth in 2106, they were led by a new Emperor Dalek. This Emperor was different to the Time War Emperor, as it was able to form a sphere and it's weaponry is much larger. This new Emperor wanted to completely change time by using a piece of the Eternity Clock, and remove Gallifrey from existence, the Dalek's would then become the new Lords of Time. The Eleventh Doctor and River Song were able to remove the piece of the Eternity Clock from the Dalek's possession, and stop them from taking over Earth and changing time. Whether this Emperor was created after the invasion is unclear, so this Emperor could still exist. (VG: Doctor Who: The Eternity Clock)

Other Dalek Emperors

 * A Dalek Emperor, described similarly to the Emperor in The Evil of the Daleks, appears in the Telos novella The Dalek Factor by Simon Clark. It is referred to as "an" Emperor, implying there was more than one at that time.
 * A Dalek Emperor was the subject of The Emperor Dalek's New Clothes, a bedtime story which the Eleventh Doctor claimed to have heard in his childhood. (DW: Night Terrors)

The Dalek Handbook
According to the non-narrative material Doctor Who: The Dalek Handbook, the Emperor in the Dalek City survived the Great Civil War and would revamp the Dalek command structure, as well as focus his strategies on rewriting the Dalek timeline.