D is for... Dalek Caan

One of the members of the Cult of Skaro, a quartet of Daleks who were assigned to devise new strategies to help win the Time War against the Time Lords and their allies. Allowed names, they had complete freedom to think up ways of winning the conflict, answerable only to themselves. Sensing that they were on the brink of defeat, the Cult removed themselves from the War by hiding in a Void Ship, taking with them a captured Time Lord prison capsule. They dubbed this the Genesis Ark, as once opened it would unleash a whole new army of Daleks. The ship was captured by the Torchwood Institute in London after it emerged from a breach between two parallel universes. The Cult emerged just as the Earth was being invaded by an army of Cybermen who had crossed the Void in the ship's wake. Caan and his colleagues used an emergency temporal shift to escape being pulled into the Void along with their army and the Cybermen.
They arrived in New York in the early 20th Century. Hiding in the city's sewers, they infiltrated the construction of the Empire State Building, intending to use it to capture a massive gamma radiation flare that was due to strike the planet. This energy would be used to fuse Dalek and human DNA to create an army of human-Dalek hybrids. The Cult's leader, Sec, experimented on himself to create a full Dalek-Human hybrid. Caan and his colleagues Jast and Thay were appalled by this development, feeling that Sec was no longer pure Dalek and therefore unfit to lead them. They rebelled against him. Caan remained behind at their base, linked to their battle computers, whilst Jast and Thay took Sec to confront the Doctor at a nearby theatre. The Doctor's DNA had become mixed with the Dalek and human DNA, so that the army no longer blindly followed Dalek commands. They turned on Jast and Thay after Sec had sacrificed himself to save the Doctor. Both Daleks were destroyed, but Caan self-destructed the army. Now the last survivor of the Dalek race, the Doctor confronted him, hoping that it would allow him to take it away from Earth. Instead, Caan activated a further temporal shift and fled.

This second shift took him back into the heart of the Time War. He was able to rescue Davros from his command ship just before it was destroyed. The effort smashed open Caan's casing, and left him mentally unsound. He began to have visions and to speak in prophesies. Davros created a new Dalek army from his own cells, led by a new Dalek Supreme. The Supreme regarded Caan as an abomination, but chose to keep him alive in a vault alongside their creator. Caan appeared to be predicting Dalek victory and the defeat of the Doctor, but what he had really seen was the evil of his own race and their inevitable destruction. He was secretly engineering the defeat of his own kind.
One of Caan's prophesies had revolved around Donna Noble - that she would bring about the Daleks' destruction, but at the cost of her own life. Caan was destroyed when the Dalek Crucible was blown up by Donna and the half-human Doctor. Donna did indeed die as a result, in that the Doctor had to wipe her memories and restore the personality she had before she met him.

Appearances: The Army of Ghosts / Doomsday (2006), Daleks in Manhattan / Evolution of the Daleks (2007), The Stolen Earth / Journey's End (2008).