I was a big D&D geek back in late 1999 (2nd edition, played Planescape and also Forgotten Realms that veered off into Zakhara, Kara-Tur, and Spelljammer) to the early 2000s (3.5 edition, and I kept up with it to 4rth edition and then dropped it), and find the history of it interesting. So if you don't mind, share of this White Avenger character as I'm curious! (First guess is that your White Avenger is like a "white hat" paladin, assuming they had paladins in the game when you played, otherwise maybe a Lawful fighter avenging villages from monsters and evil doers.)
I know very little of 1st edition and what came before, though I did enjoy reading some of the old material for the Mystara campaign (which I think was cancelled by the time of 2nd edition and even predates 1st edition). That "Hollow World" of Mystara was brilliant in design, and changed my mind that the early D&D was just a bunch of dice rolling over endless fights with almost no story or character development (other than power level) like some shoot 'em up video game. I don't know about anyone else, but even though I haven't played in years (nor bought any of the novels, though I've thought about it), I'd be curious to hear of your character.
As for the comic character....I have an EXTREMELY vague memory of hearing of a character that MIGHT have been the White Avenger. I've only tried a few Marvel and DC superhero comics and don't recall anything like that in what I read.
I wonder if it was a short run, similar to the Very Special Episode comics like when Spiderman does a "Say No to Drugs" or even talks about what to do if some guy tries to sexually molest you (my memory here is vague and I THINK I heard the Nostalgia Critic on YouTube talking about it, but I'm not at all sure), all of which were brief arcs quickly forgotten or ignored in the ongoing series. If that's the case then it would explain why you never heard of the character and I can't say if I have or not (and even if I did I couldn't say anything significant about him). Otherwise, it probably means readers found the story line not to their liking and it was dropped as a business decision.