Based on the character of the same name from Doctor Who (1965-66)
He has a toy panda named Hi-fi who is his mascot.
STEVEN: Look, you gave this ship a name just now, what was it?
VICKI: Tardis, T A R D I S. It stands for Time And Relative Dimensions In Space.
STEVEN: IDBI.
VICKI: What? IDBI?
STEVEN: I D B I.
VICKI: Yes?
STEVEN: It means I Don't Believe It.
(He refuses to believe that it's a time machine at first.)
Doctor: What do you think of that now, eh? A Viking helmet.
Steven: Oh, maybe.
Doctor: What do you mean, maybe? What do you think it is, a space helmet for a cow?
STEVEN: You know, I'm beginning to like the idea of being a crew member on a time machine.
VICKI: A crew member? You'll be lucky. He's the crew. We're just the passengers.
DOCTOR: Yes, and both very welcome ones, my dear.
I bet he would love the song Hey Stephen by Taylor Swift. (I once saw an edit of him to that so credit for that idea is not mine)
Played by Peter Purves