Drathro

Drathro (Also known as The Immortal) is an L3 Robot created by the sleepers to watch over them while they sleep. He makes his only appearance in the Season 16 finale.

The Doctors encounter Drathro watching over the sleepers in the secret underground station. After hearing about Drathro's creation, the Doctors manage to convince him to save the sleepers from Sutekh. Along the way, the Valeyard sends out an army of Osiran Service Robots to defeat them. Drathro manages to fight the service robots off, but the Valeyard destroys him using an exploding quill pen.

Drathro's death is not in vain, as the Doctors are able to use his remains to trap Sutekh in the time tunnel and send him far into the future, aging him to death.