From TARDIS Index File, the free Doctor Who reference.

Monstrons were a race of blue-skinned humanoids. They had robotic servants named Engibrains. Two Monstrons, Kenex and Yeq, landed on Skaro and made their base inside an extinct volcano. Their attempt to conquer the planet was defeated by the Dalek they had captured, which escaped and sacrificed its life to set off a volcanic eruption that destroyed the Monstrons. (DC: The Menace of the Monstrons)