Dalek leader (The Chase)

A Dalek leader, designated as Squad Leader, assumed command of the assassination squad sent to hunt down the First Doctor in a Dalek time machine, though they acted under the instructions of the Black Dalek and the Dalek Prime.

Biography
According to the Dalek Survival Guide, these Daleks were actually criminals forced to chronicle Dalek history as punishment. These prisoner Daleks noticed the Doctor using a Time-Space Visualiser before being pursued by a squad of Daleks they recognised as their future selves. They knew such a machine was scientifically impossible, but in order to ensure their future freedom, they built what would serve as an apparent Time-Space Visualiser that actually displayed recordings of the Daleks' human slaves performing reenactments of the events they knew the Doctor and his companions would view.

The criminal Daleks smuggled themselves out of prison, but were allowed to continue their plan by the Dalek Supreme, who knew they were incompetent and broadcast their attempt for the amusement of other Dalek chroniclers. The criminal Daleks left their fake visualiser on the Xeron Space Museum for the Doctor to find. One of the Daleks was killed by a Morok curator due to not paying admission and became an exhibit, while the rest were indeed those that chased the TARDIS crew through time. (PROSE: Dalek Survival Guide)

The Dalek leader was the final surviving Dalek during the battle with the Mechanoids on Mechanus. In a last bid to kill the Doctor, the Dalek leader set the Mechanoid City to self-destruct, killing everything inside, but the Doctor ultimately escaped. (PROSE: The Chase)