If there's a backstory on this, how did Balto end up living with Boris?
Here is Simon's reply:
"You know, I can't remember now. We made the film over twenty years ago. I think the idea was that Boris had found Balto as an outcast pup, and had stayed in Nome to look after him, so not flown South with the other geese. There is a little indication of Boris being a bit of an outcast too in the small scene on the boat where they see the geese flying overhead, and Balto asks him about it, just before Muk and Luk turn up.
(Useless trivia: I animated the longshot of the geese flying myself - I couldn't bring myself to ask any animator to do such a mundane shot.)"