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Bret Vyon was a Space Security Agent who assisted the First Doctor in his quest to stop the Daleks from conquering the Solar System in 4000.
Bret was born in Mars Colony 16 in the late 40th century. In 3990, he joined the Space Security Service, made First Rank in 3995 and Second Rank in 3998. His sister, Sara Kingdom, also joined the Service. He was posted on a mission to the planet Kembel in 4000 with another agent, Kert Gantry, to investigate suspicious activity by Mavic Chen, Guardian of the Solar System. Almost suffering a similar fate to Marc Cory, Bret was saved when he met the First Doctor, who had also discovered the tape-recording of Cory's SOS message. Bret learned that Chen, the Guardian of the Solar System, had allied himself with the Daleks.
Bret stole Chen's Spar and took the Doctor, Steven Taylor, and Katarina with him in it to reach Earth in time to warn of Chen's plot. Chen had convinced Bret's sister, Sara Kingdom, that he was a traitor, and she killed him. Once Sara learned the truth, she allied with the Doctor to save Earth and avenge his death.