The Original Dalek Emperor
The Original Dalek Emperor ruled the Dalek race after their previous leader, the 'Supreme Dalek', was killed. He ruled for eons and oversaw the establishment of the Great Dalek Empire, but died at the start of the Dalek Civil War, because none of his Daleks would obey him.
He would have been good pals with Jorgey if they had met, since the Dalek Emperor treats his subjects harshly and is completely insane.
The 'Imposter' Dalek EmperorThe Next Dalek Emperor took control of the Imperial Dalek faction and turned out to be Davros, the original creator of the Daleks. Davros had been planning to create a new race of Daleks for centuries, a race that would obey him without question. He modified his Imperial Daleks to be part cybernetic, which was seen as blastphemy by the Renegade Daleks. He was ousted by the Doctor to restore order amongst the Daleks, but Davros himself was not killed.
After this, the Daleks established a smaller hierarchy of Supreme Daleks and Section Leaders, but it would not be long before war drove them to establish a centralised leadership once more...
The New Dalek Emperor
The New Dalek Emperor took control before the Time War, a war between the Daleks and the Doctor's race, the 'Time Lords'. After commanding the Dalek armies against the Time Lords across all of Time and Space, his command ship was critically damaged at the conclusion of the war and he fell through time. He eventually went insane and called himself the 'God of all Daleks'. Using Humans, the God began creating new Daleks to make an Empire but was stopped by the Doctor and was disintergrated as his flagship, the Exterminator, burnt to cinders. Since then, there has been no more Emperors, but there has been another line of Supreme Daleks and even a Dalek Prime Minister.