Jeremy Fitzoliver

Jeremy Fitzoliver was a upper-class photographer and occasional companion of the Third Doctor, first got involved with his affairs through his colleague, Sarah Jane Smith. (BBCR: The Paradise of Death)

Biography
He was not that popular at the Metropolitan magazine and Sarah herself could barely stand him. He got the job mainly because his father is a majority shareholder of the magazine's publisher. (PDA: Island of Death)

It is hinted that he lost his memory messing around with one of the Doctor's inventions, and that he became the antagonist "John Doe". (PDA: Instruments of Darkness)