Ais is most always seen in pitch-black plate mail and weilding a red-scythe. While his flesh has not completely rotted away, one of his arms is completely bone, similar to that of a Pale Master's. His head is hooded and masked, leaving only two glowing eyes and a forehead revealed.
Warning: Plot spoilers begin here.
Leonhard Strembervolter was once a Paladin serving Mystra, following his father's legacy and inheriting his research in magic. Given the dark origins of some parts of this research, it was left until a later date.
Leonhard also was to be wed with his fiance, whose name has yet to be clarified. His fiance had great ambitions and she encouraged Leonhard to research more into his father's studies. Leonhard, slowly falling to her whims, did so.
This was to be her undoing, however. Sometime after Leonhard leaving the Paladin's course, a miscast of this magic caused a large swarm of meteors to crash down onto their small staying in the Skull Crags. One meteor injured Leonhard's body badly.
In an attempt to undo this mistake, Leonhard attempted to use the magic again, but to no avail. He instead created a dangerous purple mist known as Petrification Fog that spread around his current home.
In no time flat, his fiance had turned into stone.
Petrification Fog, while effective at keeping things out, and not affecting the soul it is bound to, does affect everything else that breaths. If breathed in too much, it has the side-effect of turning the poor soul into stone permanently, until undone.
Leonhard's fiance was unfortunately not so lucky, being the first victim. By some unknown circumstance, she remained encased in stone forever.
In his older years, Leonhard knew he might die at any time, and decided to use his considerable talents in Necromantic magics and creation, ascended into lich hood, and took on the alias of Ais, seeking to prevent him from shaming his once proud family name.
Spoilers end here.
Familiar: Malaki (Raven)
The Ais plot was left on a sudden hook, left unfinished. It is unclear at this point if the plot is finished, and its main character dead, or not.