For me, it would be "Theatre: An interactive night of horror"[1], the first interactive fiction work I ever saw. I actually did email him 20+ years after it was published, asking for permission to remake it non-commercially, and he was like "yeah ok whatever". I haven't really gone anywhere with that, but perhaps one day I will.
(What's more shocking is that he came from the same country as me and his company was named after a place I'd actually been to. That doesn't happen very often.)
I've never played it, but it looks fun and as somebody who grew up in the age of CYOA (Choose Your Own Adventure Books) I love the interactive fiction genre.
(What's more shocking is that he came from the same country as me and his company was named after a place I'd actually been to. That doesn't happen very often.)
[1] https://ifdb.org/viewgame?id=bv8of8y9xeo7307g