Zeno (Doctor Who and the Day of the Daleks)

The Senior Guard was the head of the guaqrds who was loyal to the Daleks in an alternate 22nd century. After overhearing the Controller talking to the Doctor and Jo Grant about preventing the Dalek invasion of Earth and the Controller betraying the Daleks, he informed on the Controller. When the Daleks exterminated the Controller, the Senior Guard was made the new Controller. (DW: Day of the Daleks)