Gwanzulum

The Gwanzulum were a shape-shifting species stranded on the planet Adeki.

Biology
In their natural form, the Gwanzulum appeared as large, monstrous heads with muscular, stubby arms and legs.

The Gwanzulum were telepaths, who could read their target's mind and take take the form of individuals from their target's memories. They were parasitic energy leeches, draining life-force from and ultimately killing their targets.

History
The Gwanzulum were the oldest shape-shifting race, predating the Whifferdills and the Kymbra. During a conflict known as the Shaper Wars, the Gwanzulum all but wiped out the Whifferdills. The wars ended with the last of the Gwanzulum being stranded on the planet Adeki. They drained the life force of the Adeki natives, and remained alone on the planet.

The Doctor encountered the Gwanzulum when he stopped on Adeki for a fishing trip. Reading the Doctor's mind and beginning to feed off his life-force, the Gwanzulum took the forms of the Doctor's past companions and selves in order to trick him into letting them aboard the TARDIS. Having learned of the Shaper Wars from carvings in a tunnel wall, the Doctor saw through the Gwanzulum's deception and made his escape alone. (DWM: Planet of the Dead)

Behind the scenes
The Gwanzulum were an idea by John Freeman that Richard Starkings decided to use across almost every Marvel UK comic at the same time, Doctor Who Monthly included. Among their other notable appearances were the Combat Colin segments of The Transformers comics.