Magos

Magos was a Time Lord Cardinal who lived thousands of years before the Doctor and the Master's time period. The Master believed him to be one of Gallifrey's greatest scientists, unappreciated at his time, though the Doctor regarded him as a sociopath as well.

Biography
Magos was put on trial by the High Council after he carried out experiments resurrecting the dead as automatons. He was sentenced to banishment.

In exile, Magos created the Cognition Shift which he hid on Nastrum. He used automatons to take over Kurnos 5, ruling from a castle where he set up a laboratory. He sired many children during this time. Magos was eventually overthrown by the natives, with his rule passing into legend. (AUDIO: The Castle of Kurnos 5)

Post mortem
Magos' tomb was found by during the Last Great Time War, who brought his body to the abandoned castle on Kurnos 5. The Master identified a descendent of Magos, using her body to briefly resurrect Magos in. He asked Magos for the location of the Cognition Shift, which Magos supplied after approving of the Master's intent to use it on "everyone". Afterwards the Master let him return to death, believing from their conversation that Magos actually enjoyed being dead, and subsequently destroyed his body. (AUDIO: The Castle of Kurnos 5)