Vassarian

 was a Time Lord soldier whose Battle TARDIS was damaged by a Dalek attack. He managed to eject his Eternity Cage from his TARDIS whilst it repaired itself but he started to regenerate and was placed in stasis without the process completing. Spending so long in this state however burnet through all his regenerations. In this state he was leaking artron energy, attracting a Sontaran scouting party. Aware enough of his surroundings to understand what the Sontarans were trying to do him, Vassarian, wanting revenge on them, manipulated his captors, feeding them information enough on how to harness the artron energy in the hopes that they would summon the Dalek Empire who would destroy the Sontarans.

When the Daleks came to Rovidia, Vassarian was too weak to dissipate the artron energy. Instead, Vassarian reached out to the War Doctor, guiding his fellow Time Lords to him. When they arrived at the laboratory where was being, Vassarian explained his intentions to the Doctor and instructed the Doctor to escape in his TARDIS. When the Fesk then threatened Kalan, Vassarian turned the artron energy on the Sontarans before he and the Doctor dissipated the artron energy, lowering the defences holding back the Daleks. With the last of his strength expended, Vassarian died as the Eternity Cage shut down. (AUDIO: The Eternity Cage)