Zeno (Doctor Who and the Day of the Daleks)

The senior guard was the head of the guards who was loyal to the Daleks on an alternate 22nd century Earth.

After overhearing the Controller talking to the Third Doctor and Jo Grant about preventing the Dalek invasion of Earth and the Controller betraying the Daleks, he informed his masters of the Controller's treachery.

After the Daleks exterminated the Controller as a traitor, the senior guard was made his replacement. (TV: Day of the Daleks)