Galvatron

Galvatron was a mechanoid and a Transformer who had a history with the Freelance Peacekeeping Agent Death's Head. When Galvatron traveled back into Earth history, Death's Head followed him to obtain a bounty. (COMIC: Meet Death's Head)

Clara Oswald once played with a toy which resembled Galvatron. (TV: The Crimson Horror)

Behind the scenes
The toy robot which Clara plays with in The Crimson Horror is the original G1 Galvatron figure from 1986. This stands somewhat at odds with COMIC: Meet Death's Head, which implies that The Transformers and Doctor Who take place in the same "universe." However, The Incomplete Death's Head retcons that the "Robot universe" was actually a separate reality from the Doctor's.

G1 Galvatron was voiced by Leonard Nimoy in The Transformers: The Movie (in which Galvatron made his debut), and by Megatron voice actor Frank Welker in The Transformers seasons 3 and 4.