Monterey Jack was my PC when I first started playing Cthulhu back in 1982. He was an obvious ripoff of Indiana Jones, and, as I was 13 at the time, I never really developed much of a backstory for him. It was enough to just know he was a college professor of Archeology at MU and he had a bullwhip and was "cool."
He was well-known in our group for going mad at the drop of a hat (mostly due to my complete inability to roll dice well). As such, he was a great "catalyst" for adventure sessions. He was fascinated with the mythos, so would gather all these tidbits, then assemble a team and lead them into the unknown. He always wanted to "find out more" so as soon as there was a hint of a monster, he'd charge right in, see it, go insane, and then I'd bring in my backup PC.
He was notable for sneaking into the basement of the Silver Twilight Lodge (SoYS), learning the Ressurection spell, mixing all the urns of Essential Saltes together and casting the spell. Which created a horrible monster of "parts" of guys, caused him to take a 1d6/1d20 SAN test, which of course he failed...
He also lasted about two minutes into Masks of Nyarlathotep. And of course Sandy's infamous "Moth Man" scenario... I think he lasted up until the "flogging" scene, then went nuts... He led a team back there many years later, and encountered some sort of monstrous jereusalem cricket beastie in the coal mine... and went nuts... You'll have to ask Sandy about that one... I'll see if I can scare him up.
Monty fought Dracula in the Carpathian mountains, alongside Sherlock Holmes in a scenario run by Larry DiTillio at a convention... all sorts of other wacky shennanigans as well.
Plenty of other great adventures as well. I still keep his sheet around in case I ever get to play another 1920's era adventure.
As far as notable appearances in gaming books, he was mentioned in half a dozen Cthulhu books, as well as being one of the 6 main characters in Arkham Horror, and I beleive even got a mention in the Ghostbusters RPG. Obviously that must have been his grandson or something.
As far as the name goes... well, I grew up in the San Francisco Bay Area, found some Monterey Jack cheese in the fridge one day and thought that'd be a funny name for an Indiana Jones parody... it stuck... Originally, it was just Monterey Jack, but then one of "The Guys" pointed out that that was a dumb name, because Jack was a first name. So Sandy and I conferred and came up with the last name Terwilliger (from "The 5,000 Fingers of Dr. T") which we agreed was the worst name ever, and would explain why he never used it.
Look, lots of things are funnier when you're 13...