Arunzell

 was a Tolian. He told the Seventh Doctor and Raine Creevy about the plight of his people, persuading them to re-energise his race using the final node activator in existence. Threatening to kill Raine, he forced the Doctor to open a dimensional rift, which resulted in the balance of dimensional energies becoming unstable. He then entered an alliance with, working with him to become the masters of all dimensions through their biology being rewritten by the Master using dimensional energies. After the Doctor revealed to him that the Master had planted the dimensional node on their world in the first place, he betrayed him and enabled the Doctor to escape in his TARDIS. With the balance of the dimensional energies restored, he shrunk back to his normal size, allowing the Master to kill him with his Tissue Compression Eliminator. (AUDIO: UNIT: Dominion)