Steven was a unique companion in many ways. Every time the TV show, novels, or audios try to invent a new companion with some unique twist, they realize that Steven already did that twist. 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.