Having written the story, I decided my characterisation wasn't that great and that I might not have got across the aspects I wanted to put into Ulin's character... so in addition, I've done this page, which simply describes him. (For the hell of it; I don't see any practical use for this "information", and any time TSR release another novel with Ulin in, they'll probably do something completely different. I would really love if they use this, though, and I'll certainly give my permission if needed... it's just rather unlikely, unfortunately :)
Most of this is simply made up by me, although it's certainly based on what few hints we have about his character from Rabe's books. Where I remembered the appropriate bits, I've noted them. [This means there are some very minor spoilers to Rabe's books.]
From an early age, Ulin was captivated by the stories and legends about magic; mostly, by the way a single person could wield such power. He doesn't have any strong idea about what he would use such power for - unlike many mages, he doesn't have a troubled childhood, he is good-looking, etc., so there is no "I'll show those bastards who made fun of me" motive.
Why this interest? Well, of course, his father is one of the most powerful mages on Krynn and he is the one that Ulin consciously looks up to. Subconsciously, though, he is more interested in his great-uncle; after all, Raistlin was most likely the most powerful mage of all time... The example of a mortal being in a position to become a god is still relevant now the gods have left.
(Rabe had a conflict between him studying magic with the gold dragon, and being with his wife & children...it looked like he was choosing magic, where he had to make the choice...)
Ulin isn't really a "good" person in the way that many of the original Companions were. He tends to follow actions that you'd expect of such a person, sure. But that's simply because he's been brought up by two people who would never consider any other action. He hasn't really even seen that there are alternative ways to behave, never mind been tested in any way.
He tends to forget to consider others sometimes, figuring they can get along okay, and being more concerned with himself. (Same example from Rabe.)
If he was more thoroughly tested in some way... who knows how he might turn out?
Ulin's feelings aren't a primary concern with him. He may be in love, but that wouldn't be the over-riding priority as it is with some others; he can easily put it aside. He might find it difficult to tell "love" from "friendship". (He can recognise lust, though, I'm not saying he's completely useless ;)
As already indicated, considering the feelings of others isn't something that comes naturally to him. He probably wouldn't intentionally try to hurt their feelings, but he would consider it silly of them to be hurt - after all, he didn't mean to hurt them by whatever he said or did.
(Example: the family thing. Again. :) Somebody goes on at him about this, I think Goldmoon or Usha, forget which.)
Ulin tends to make snap decisions and act on them, basically according to how he feels. He's unlikely to worry about whether other people think it's a good idea. (Although he isn't honestly arrogant - he wouldn't claim, if asked, that his own opinions are always more valuable than others - he just tends not to take other people's opinions into consideration, doesn't even think about them.)
(Example from Rabe's books when he does something stupid, in collaboration with Rig I think, sets fire to KoT ship or something...)
(If you haven't figured out where this is leading yet, where've you been...? ;)
Basically, Ulin needs to grow up in a lot of ways. I don't care if he is 30... I think his probably-sheltered upbringing didn't manage to curb those problem tendencies. What happens to him, when there are hard decisions to be made, should be interesting... [Except, of course, that I'm not going to write anything more about him - sorry, but I'm trying to write stories that I can actually get published, i.e. where TSR doesn't own the world and main character :) - and whoever at TSR does end up writing about Ulin next will probably treat him totally differently from my ideas. Oh well. :)