Throughout the Daleks' history, they have often been led by an Emperor. How exactly the Daleks appoint their leaders is unclear, but Emperors are typically distinguishable from normal Daleks by having unique shells. At least six Emperors are known to have existed:-
Dalek Prime - The first Dalek to be created on Skaro by Davros himself. This Dalek was the one that supposedly killed Davros and exclaimed the Daleks' superiority over the rest of the universe. Prior to the events of the Doctor Who novel War Of The Daleks, the Dalek Prime had been named Emperor.
Golden Emperor - Following the aftermath of Skaro's Neutronic War, only a handful of humanoid Daleks remained and were persuaded by their 'encased' descendants to build more shells for them. Before they died, the humanoids built a golden shell for the Emperor to reflect its rank. The upper casing was an oversized sphere, with the lower casing being the same shape as all other Dalek shells.
Emperor Within the Dalek City - This Emperor appeared in the Second Doctor story, The Evil of the Daleks. It dwelled within a huge, immobile shell deep within the Dalek City on the planet Skaro and was apparently destroyed during a civil war between its own standard Daleks and a group of "humanised" Daleks. At the end of the story arc, a flickering light was seen, indicating that the Emperor was still alive.
Davros- In the Seventh Doctor story Remembrance of the Daleks, Davros had been established as Emperor of the Imperial Dalek faction. His body was completely encased in a large white spherical shell. He demanded that the Doctor surrender the Time Lord weapon - the Hand of Omega - to him, otherwise he would destroy Earth. However, when the Hand was activated, it travelled to Skaro and destroyed the whole planet, then returned to destroy Davros's ship. Davros escaped, but his entire army was obliterated.
The God of All Daleks - This Emperor commanded all Dalek forces during the Last Great Time War. When the Doctor launched his endgame strategy to destroy both the Daleks and the Time Lords, the Emperor's flagship just barely managed to escape and fell through the time vortex. It emerged in the dark space just beyond the Sol system, during the Fourth Great Bountiful Human Empire. Over the centuries, the Emperor's remaining forces quietly infiltrated the Empire's systems, manipulating mankind's progress through alien intermediates such as the Jagrafess. Using cells harvested from human prisoners and social outcasts, the Emperor created its new Dalek army, proclaiming itself to be the "God" of all Daleks. In the year 100100, the Daleks had built a fleet of 200 ships and an army of over half a million. When discovered by the Ninth Doctor, they launched an invasion of Earth and bombed whole continents back to the stone age. The invading Daleks and their Emperor were all destroyed at the last minute by Rose Tyler - the Bad Wolf - who had absorbed the power of the Time Vortex and used it to annihilate them all.
The New Emperor - Following the creation of the New Dalek Paradigm, the Progenitor Daleks travelled back into their own history and rebuilt Skaro. They rebuilt their city of Kaalann and created a new Emperor to lead them, which was housed in the same immobile shell as the last Emperor. However, the Eleventh Doctor used the Eye of Time to undo the Progenitor Daleks' meddling, and so the Emperor was never created.
