Kamelion

Shape-changing android which the Master took with him when he escaped from Xeriphas. He was a tool, used by an earlier invader of Xeriphas. The Master used Kamelion to impersonate King John of England in an attempt to prevent the signing of the Magna Carta, but was thwarted by the Fifth Doctor who took over control of the android in mental battle (6J). Kamelion stayed with the Doctor in the TARDIS. But the Master succeeded in re-establishing control of him and used the android to bring the Doctor to Sarn. He first assumed Prof. Foster's likeness, then turned into the Master. In the end, he begged the Fifth Doctor to destroy him with the Tissue Compression Eliminator.