Note: I call a character a main character when he/she plays in 2 or more MI-games. Murray is an exception, but I think that when there will be a MI4, Murray will be in it...
This Guy is Guybrush Threepwood. He is about twenty years old. He is a pirate, and is-after MI3-married with Elaine Marley. He is THE main-character. And-don't ask ME why-he hates porcelain...
LeChuck is the bad guy of the MI-series. He seemes to be the brother of Guybrush (his name is Chuckie Threepwood) or is this brotherhood stuff not true? Well, it doesn't matter. He is in love with Elaine, but Elaine hates him. Maybe this is because LeChuck is dead? In MI1 he was 'the ghostpirate', in MI2 he was 'the zombiepirate' and in MI3 'the demonpirate'.
Elaine Marley is the woman of Guybrush (after MI3), but LeChuck is in love with her too. This sometimes gives some troubles. In MI1 LeChuck kidnapped Elaine, in MI2 LeChuck almost killed Guybrush (by the way: in MI1 too, it's just that nobody dies in the MI-series), and in MI3 LeChuck changed Elaine in a golden statue. Well, he didn't did this really, Guybrush just found a huge cursed ring on LeChuck's ship and gave this to Elaine...
Elaine is the governor of Mêlée-, Booty and Plunder Island.
The Monkey Island Canniballs. From the left to the right: Lemonhead, Bananahead and Pinehead. They play in MI1 and MI3. These guys are not really dangerous: they are vegetarians...
This is the Voodoo-lady. She has helped Guybrush always very much with her voodoo. In MI1 she's on Mêlée Island, in MI2 in a shack in a swamp on Scabb Island and in MI3 in a ship in a swamp on Plunder Island.
Wally B. Feed
Wally lived in woodtick on Scabb Island and he was a cartographer. He was searching for Big Whoop. His live was peacefull until...he met Guybrush Threepwood. LeChuck kidnapped him to distract Guybrush. Guybrush and Wally were both prisoners of LeChuck but they knew to escape. Guybrush exploded LeChuck's fortress and was thrown on Dinky Island. Without Wally. Wally followed 'how to become a pirate' lessons by LeChuck and got himself a tattoo, changed his name into 'Pirate Bloodnose', and helped LeChuck. Then his life was really cool until...he met Guybrush again. Guybrush said to Wally that he's a failure as a pirate and Wally removed his tattoo on Plunder Island, and stopped pirating. He plays in MI2 and MI3.
This is Murray, the demonic skull (isn't he cool!). Guybrush shoots his boat with a canon and that's how Murray lost his body. Now he wants Guybrush' body to rule the world, or haunt people so they can never anymore find socks that match...things like that. That's why he always asks Guybrush if he's dead already. He only plays in MI3 but I really think he'll return in MI4.
Stan is a really irritating salesman. He sells previously owned vessels in MI1, previously owned coffins in MI2 and life-insurances in MI3.
I think Herman Toothrot is really the most irritating person in the Monkey Island series. He came on Monkey Island with 'the Sea Monkey' but he stranded, now he was officially a shipwreckling. So he trained some monkeys and sended them back to Mêlée Island to get help. He talks really much. In MI2 he has a philosophy class on Dinky Island. In MI3 he's only a part of an attraction in the Big Whoop carnival. (Guybrush: "That one doesn't talk, thank you technology")
The men of low fiber (pirates) play in MI1 and MI2. They are very strange, and their businnes isn't really legal (if you ask me- and no one does so I just tell you). One of them, the one on the left, has a rat. Guybrush likes rats, especially in a light wine sauce.