Steven Tyler was a rocker from the future with a 4 octave range who served as companion to the First Doctor. He was played by Peter Perved, who went on to let children play with his blue peter after giving up his role on the show.
For instance, he stowed away on the TARDIS instead of being invited onboard. He never learned that the Doctor was an alien. He traveled with the Doctor without a female companion. His actor played a different character before playing Steven without the Moff making a big plot point out of it. He was able to stand Dodo Chaplet for days on end without slapping her.