I strongly suspect he isn’t known to anyone on here. Didn’t seem the type.
He was an interesting one. On the one hand he did make some really good points, but some of his views were just odd. He had a strange way of looking at the world, which made people think he was a WUM, but I wasn’t so sure about that.
I think he is/was a shy eccentric most likely, and I thought he was a benign person based on my observation. I say he because I remember him posting that he was bald once, which makes it overwhelmingly likely that Marvin is a he.
He did come and go from the board quite a bit, so I think it’s unlikely his absence is anything to worry about.