Greg Stillson (first appeared in The Dead Zone)

Greg Stillson is mentioned in the following books:

The Dark Tower VII: The Dark Tower (Sep 2004)

“GMS stands for general mentation systems,” said Nigel. “There are two such systems, rational and irrational. Conscious and subconscious, as you might say. As for Greg, that would be Greg Stillson, a character in a novel I’m reading. Quite enjoyable. It’s called The Dead Zone, by Stephen King. As to why I bring him up in this context, I have no idea.”
- Part 2 / Chapter II / Section 1