Karen Brett was an admiral in the Earth Empire military during the Orion War in the 26th century. She became President of Earth after President Duncan Levinson's assassination. She then asked Liam Barnaby to investigate the Scorpius organisation. (AUDIO: Scorpius)

She started to become influenced by Paul Hunt about the policies she pursued. She also dismissed Liam's warnings about Paul and the Scorpius organisation and fired him from his position in the Army. She sanctioned the conversion of refugees into Cybermen. (AUDIO: Fear)

Shortly afterwards, she was persuaded by Paul to place the Cybermen on the streets of Earth for protection and told the populace that she was going to lead a mission into the android controlled zone as a final strike. She was then converted into a Cyber-Leader. (AUDIO: Conversion)

She was sent on a mission to Telos in order to activate the tomb there which would then activate all cybertombs. She met with an android ship there and died in the attack. (AUDIO: Telos)