The thing is there IS a level of canon info we know from Blood in Baldur's Gate.
We know that they were a
serial killer, and that they could use magic to hide their tracks, making them a caster of some sort. I THINK they referenced them being a sorcerer, but I'm not sure, I'd have to read through it again. EDIT: Yup, they were a sorcerer.
For the people saying there is no "canonical" class and race, you're both right and wrong.
In terms of YOUR experience with the game, that's true.
In terms of the lore on it's own, he is canonically a
white scaled dragonborn sorcerer.