This topic has always been interesting to me. This will probably be a primarily ghost-focused thread by its nature, but I'm interested in things like Kadabra as well. Which pokemon do we know for sure were human? I can think of the Gengar line, the Cofagrigus line, and the Trevenant line. I always assumed that the majority of pure ghost types or ghosts that always carried ghost typing were actual ghosts of something, but I generally assumed they were the ghosts of pokemon and was surprised to learn Gengar is a human's ghost.

For that matter, what of such situations as a Gardevoir's trainer dying and becoming a Gastly? Would Gardevoir still stand by them and just deal with a lifetime of just doing Gengar things?