It’s a tossup between three of them. First, is Endeleban Losteast (Delban). He’s a wizard and former Aes Saidarr of Cormyr. He was the second character I played with the Wyrmfang Chronicles as we adventured through the dream realm of Ravenloft. It was there he made a mortal enemy of the death knight Soth and gained a Tome of Evil that he made use of later in a quest for power. After turning to evil, he entered the state of NPC-dom, making 3 or 4 appearances over the years before eventually returning to a PC status for a jaunt though the Underdark in the City of the Spider Queen trek. It was during this trek that he cast off the powers of evil that he gained for more neutral status and a future unknown.
Second is the paladin Terun Eastmore. As a paladin of Helm, he followed a path slightly adjacent to what most paladin’s might call correct. In 3/3.5e Forgotten Realms, paladins of Helm are concerned only with destroying evil where they find it, sometimes with a disregard for helping those in need or who might be deemed innocent. This led to some strife within the party and he eventually left to find his own path. He also lost an arm along the way, leading to endless jokes about the one-armed paladin in the party.
The last one is Aeduin, the cleric (former bard) of Occipitus. I mentioned him a bit in Day 6 and he’s the only character I’ve played through to level 20. He was last seen taking ownership of the Inn Between Worlds and giving it a permanent home on Occipitus. Little is known about what’s happening there but word is that Occipitus is quickly becoming known as neutral ground where all may gather without concern for too much trouble.