The friendly ghost with the friendly most, look out, cuz things are gonna get tubular! It's Jasper, played by Griffin McElroy, who did I mention is dead? Yep, he's a victim of the 90's, they always were a rough decade.
Real talk, I know some people were disappointed by the lack of a Jasper episode in Season 4, and in fact I was taken aback by it too, but I think if Season 3's "Dial M for Jasper" is where the arc ends, I'm satisfied. David accepted he made his mistakes and learned from them, and Jasper retroactively forgave David. I don't know if we quite need an episode where David learns the hard truth, unless we need an excuse for him to really stick it to Cameron, though given how the 20th anniversary special started, methinks that ship has sailed for now.