Dalek Prime

During the Last Great Time War, a Dalek Emperor resided in Kaalann on Skaro. (GAME: City of the Daleks)

Origins
According to the research of human historians of the Daleks, a new Dalek Emperor took over the Imperial Dalek faction after Davros was lost (though not actually killed) in the explosion of Skaro's second sun (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) caused by his activation of the sabotaged Hand of Omega in 1963. (TV: Remembrance of the Daleks) He carried forward Davros's long-held plan to move against the High Council of the Time Lords, thus beginning the Great Time War. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)

According to another account, while Davros did survive, the Imperial Daleks were completely annihilated in the explosion. The surviving Emperor who returned to a resurrected Skaro at the height of his power was in fact the leader of the Renegade Daleks, the Dalek Prime himself. (PROSE: War of the Daleks)

Lead-up to the Time War
The Dalek Emperor resided in his throne room within the Dalek City on Skaro, protected by the Imperial Guard Daleks. The Daleks' strategy computers and assessment engines predicted an incoming war, that would rage throughout all time and space, against an "ancient enemy" that was potentially a match. Believing that the coming conflict would take every resource and stratagem just to survive, the Emperor sought to ensure victory by employing new methods, daring to even question what it was to be a Dalek. As such, the Emperor gave an order with his unique ident codes to summon four high-ranking bronze Daleks, all of whom were deemed to have demonstrated abilities above and beyond the simple execution of orders as they used initiative to emerge successful in every endeavour, to meet with him: the Commandant of Station Alpha, an Attack Squad Leader in the Thirtieth Assault Group, the Force Leader of the Outer Rim Defensive Batallion and lastly the Dalek Commander of the Seventh Incursion Squad, whose order came just after he had saw to the extermination of the Mechonoids.

Explaining their new purpose as a weapon, the Emperor announced that that they were to be reconditioned to enable them to think as no Dalek had ever been able to think, to think and become like the enemy, daring to plan and act in ways that no other Dalek, even himself, would countenance. Designating them as the Cult of Skaro, the Emperor chose to name the four Daleks Thay, Caan, Jast and Sec, the latter being the leader of the Cult. On the Emperor's order, the Cult were escorted to the Weapons Factory to be fitted with the latest armour and weaponry, while a unique black casing composed of Metalert was prepared for Dalek Sec. (PROSE: Birth of a Legend) The Cult of Skaro were to become a legend during the war, "above and beyond the Emperor himself". (TV: Doomsday)

The Last Great Time War
During the early part of the Time War, the Emperor was informed by the Dalek Time Strategist about Project Revenant. Romana II tried to convince him to stop the war as it would involve both sides being destroyed as a result. (AUDIO: Desperate Measures)

Because of 's activation of the Heavenly Paradigm, the Emperor took control of the Cruciform. (TV: The Sound of Drums; AUDIO: The Heavenly Paradigm) Towards the end of the War, the Emperor oversaw the creation of the Eternity Circle, and was present when they created the Temporal Cannon to use against the Time Lords. The Emperor witnessed the other temporal weapons used against human prisoners, like the former governor to Moldox, Jocelyn Harris who had betrayed her people to work for the Daleks as their puppet. The Emperor watched as Jocelyn was removed from history as a demonstration. (PROSE: Engines of War) When Skaro was devastated, the Emperor was thought to have been killed. (GAME: City of the Daleks)

The Dalek Emperor was aboard his saucer flagship when all thirteen incarnations of the Doctor moved Gallifrey to a pocket universe on the last day of the Time War. The assembled Dalek Fleet ended up firing on itself through the space Gallifrey once occupied, an event which was presumed to have been the activation of the Moment; (TV: The Day of the Doctor) as such, the Emperor was believed to have died with the rest of his species, but this was mistaken. (TV: The Parting of the Ways)

After the Time War
The Emperor's lone ship barely survived the Time War, falling through time in a heavily damaged state. The nine-metre tall Emperor's new casing had the appearance of his Kaled mutant revealed 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. He went into seclusion at the edge of the solar system "damaged but rebuilding" during the Fourth Great and Bountiful Human Empire while he used any humans that stumbled upon him to create a new army of Daleks, and he steadily rebuilt his fleet.

Circa 199,909, he secretly installed the Jagrafess aboard Satellite Five to play the "long game" of slowly manipulating humans and re-establishing the Dalek species and fleet. A hundred years after the Jagrafess was killed, in the year 200,100, the Emperor was still using Satellite Five, now renamed the "Game Station" to manipulate humanity and conceal a Dalek fleet. (TV: Bad Wolf) The Emperor secretly used transmat technology aboard the space station to kidnap humans for nearly two hundred years. The kidnapped humans were harvested for their genetic material, and "one cell in a billion" was used to rebuild a new race of Daleks (TV: The Parting of the Ways) numbering roughly half a million aboard a fleet of 200 ships in just a century. (TV: Bad Wolf)

Because the Emperor had recreated the Dalek race, he saw himself as a god and immortal and so was worshipped by the new Daleks. These and other religious concepts such as blasphemy were new to Dalek psychology. The Emperor had become insane due to the fact he had been in hiding for so many centuries. (TV: The Parting of the Ways)

The Emperor's pawn aboard Satellite Five, the Controller, hated her masters and transmatted the Ninth Doctor aboard the Game Station to help defeat them. (TV: Bad Wolf) When he encountered the Emperor and his new religiously fanatical Daleks, the Doctor surmised that they were driven insane both because they had isolated themselves for so long, but also because they were in denial of the fact that they were part human. The Daleks killed almost everyone aboard Satellite Five, and they attacked Earth, bombing millions of people, to transform it into the Emperor's "temple". Shortly afterwards, the Doctor turned down his chance to use an uncalibrated delta wave to destroy all nearby life, human and Dalek alike. The Emperor thought he was victorious, but he and his entire fleet were atomised by Rose Tyler after she had absorbed the energies of the time vortex and became the Bad Wolf temporal paradox; (TV: The Parting of the Ways) she later described what she did as "pouring the Time Vortex into his head and turning him into dust". (TV: Doomsday)

Post-mortem
While competing with Sarah Jane Smith over their adventures with the Doctor, Rose Tyler one-upped her when she said she faced Daleks by noting that she had "met the Emperor". (TV: School Reunion)

Rose would later gloat over her destruction of the Emperor which she revealed in her confrontation with Dalek Sec, enraging him to the point that he was only stopped short of exterminating her by the arrival of the Tenth Doctor. (TV: Doomsday)

recalled the Emperor's conquest of the Cruciform whilst revealing to the Doctor what became of himself during the Time War. (TV: The Sound of Drums)

This Emperor's casing on Skaro was used by the New Dalek Paradigm to create a new Dalek Emperor who resembled his predecessor. (GAME: City of the Daleks)

Behind the scenes
A Dalek Emperor of identical appearance, and also voiced by Nicholas Briggs with the same voice effect, appeared in the video game LEGO Dimensions, though it is not clarified whether he is the same Emperor from The Parting of the Ways, or another lookalike using an identical casing as the one from City of the Daleks. However, the game, due to its branching story, is not considered valid on the Tardis Data Core.