Transformers Universe

According to Hob's Death's Head Interactive Archive, Death's Head spent time on a parallel universe home to a war between factions of massive robots, (COMIC: The Incomplete Death's Head) who, according to another source, were known as the Transformers. (COMIC: Meet Death's Head)

History
After some time on Scarvix, Death's Head was mysteriously captured and transported through a warp gate by an unknown person to this universe. In order to battle, Death's Head's size was drastically increased. (COMIC: The Incomplete Death's Head)

At one point, Death's Head followed Galvatron, a mechanoid and a Transformer, into Earth's past in search of a bounty.

He later battled and, according to him, defeated a vast planet-devouring Transformer by attacking him on the psychic plane. (COMIC: Meet Death's Head)

Following the battle, Death's Head became trapped by the gravity well of a collapsing planet, accelerating him at "trans-temporal speeds" into the Time Vortex. (COMIC: The Incomplete Death's Head) He ended up colliding with the Seventh Doctor in his TARDIS. The Doctor shrunk Death's Head back to his original size and dumped him in the year 8162. (COMIC: The Crossroads of Time)

The Doctor later claimed to have been the one who had brought Death's Head to what he dubbed "the robot universe", in order to shape his future. (COMIC: The Incomplete Death's Head) However, Death's Head once spoke of his encounters with the Transformers as if they were in the same universe as the rest of his adventures. (COMIC: Meet Death's Head)

Behind the scenes
Though never mentioned explicitly in The Incomplete Death's Head due to licencing issues, this universe is in fact that of the. Marvel Comics has numbered it, and within the Transformers franchise it is called Primax 984.20 Gamma.