Emperor's Personal Guard

The Emperor's Personal Guard was a Dalek organisation made up of Daleks dedicated to protecting the Emperor Dalek at all costs.

History
The Emperor was always guarded by the personal guard. They were normal Daleks, but with black domes to distinguish them from the rest. (DW: The Evil of the Daleks)

During the Last Great Time War, the guards possessed a claw-like manipulator arm instead of the standard "plunger" arm, and some had a more powerful gunstick opposite the standard gunstick. (DW: The Parting of the Ways)

The Personal Guard also made up the High Council of Daleks, of which the Dalek Supreme was also a member. (REF: Doctor Who: Aliens and Enemies)

Although he was not the Emperor, Dalek X also had black-domed guards. (NSA: Prisoner of the Daleks)

Daleks with black domes are often seen taking part in battles and conflicts depicted in the Dalek Wars section of Doctor Who: Battles in Time magazines.