Great Uncle Piderman made his first appearence as a picture in the episode "Ghost Night". He apparently lived in Piderman's house a long time ago. His portrait, present under a basement strangely present on the second floor, hides a tunnel. This tunnel had the presence of That Thing and "mirrors" (probably X-Ray) that showed only the persons bones. Wanda lived in there before asking Piderman if she could live with them. Nothing else is known about Piderman's uncle, as Piderman himself didn't know about who lived there before him.