I was sorting through some boxes today and I came across my copy of Tim Power's On Stranger Tides, which I read in the late 80's and was the inspiration for Monkey Island. Some people believe the inspiration for Monkey Island came from the Pirates of the Caribbean ride - probably because I said it several times during interviews - but that was really just for the ambiance. If you read this book you can really see where Guybrush and LeChuck were plagiarized derived from, plus the heavy influence of voodoo in the game.
When I am in the early stages of designing, I'll read a lot of books, listen to a lot of music and watch a lot of movies. I'll pick up little ideas here and there. We in the business call it stealing.
This book really got me interested in pirates as a theme. Fantasy was all the rage back then and I wasn't keen on doing another D&Dish game, but pirates had a lot of what made fantasy interesting without being fantasy.
After some early failed starts I shelved the idea and began work on the Indiana Jones and the Last Crusade game. When it was finished I went back to work on Monkey Island and re-thought much of the design and story. Although re-thought is a strong word since I didn't have much to start with.
The bulk of the motivation for Guybrush's character being so naive stemmed from wanting him to know as little about the world as the player. One huge problem adventure games had/have - Police Quest being the most frustrating example for me back then - was the character was supposed to know all this information that the player didn't. I hated playing games like Police Quest where I get fired for not signing out my gun (or such such craziness), when I was supposed to be a cop. I should know that stuff? Shouldn't I?
I figured if Guybrush didn't know anything, then the player wouldn't be frustrated when they didn't know how to do basic pirate tasks. Which was the whole genesis for the opening line:
"Hi, my name is Guybrush Threepwood and I want to be a pirate"
It told the player that Guybrush didn't know any more then they did, and they were going to learn together.