Paelias Galanodel
Paelias Galanodel was a wizard who appeared in the first Tale of Quelmar (one-off) who had cynically attempted to teleport himself into The Abyss. Not realizing the complications that would arise from simply trying to teleport, Paelias became trapped in Quelmar's buffer layer, known as The Underdark. However, as the spell never fully completed, he became stuck between planes, constantly shifting between the surface, the underdark, and the abyss.
Paelias' husband, Hadarai Oakenheel, would ask several adventurers to join him on a quest to find Paelias. He would discover Olga and Vladimir Petrov, as well as a Doctor Frank N. Stein, and the four of them would locate Paelias safely, and find out where he was appearing on the surface.
A research station was set up around Paelias once they discovered his surface teleportation point. From there, during his brief appearances on the the surface, Paelias would talk to AID about what he experienced, and helped pioneer their original explorations into the Underdark.