Marty was a small pirate who lived in Tortuga.
Curse of the Black Pearl
In The Curse of the Black Pearl, he is hired by Joshamee Gibbs and Jack Sparrow as a part of the crew to reclaim the Black Pearl. He can be found in the Tortuga Mines, and will join your crew as soon as you locate his blunderbuss with Jack's wonderful compass. After that, he's all yours.
Dead Man's Chest
Marty appears again in the next chapter, but is not playable (in Story Mode) until the second level: Pantano River
At World's End
Marty again reappears to us in the third chapter, At World's End. He can be played in Singapore, and most levels after that.
Marty is a great character to play with. He is a small character, so he can crawl through small areas, and is one of the few characters who carries a weapon that can blow up silver bricks.