From Monkey Island wiki
The Cannibals are a recurring group of characters. Originally inhabiting Monkey Island, the Cannibals wear distinctly over-sized masks to make their appearance more deadly; consequently no-one has ever seen their face. In the first game they go from being antagonists to supporting characters on Guybrush's quest to rescue Elaine; in the third game they are still friendly but Guybrush must trick them in order to advance his quest.
The Secret of Monkey Island
The three cannibals introduced in this game are Red Skull, Sharp Tooth and Lemon Head. They are a group of "head-hunter gatherers" (a play on "hunter-gatherers") but very health-conscious, which is why they rarely eat people straight away. Guybrush angers them when he steals some bananas from their camp, but after making an offering (a tiny idol) to the Cannibals' item of worship, the Giant Monkey Head, they are appeased and Guybrush is allowed to come and go as he pleases.
In the game the Cannibals assist Guybrush twice. The first time they give him the Head of a Navigator which helps Guybrush navigate the Caverns of Meat beneath the island; in exchange Guybrush hands over a sailing pamphlet from Stan entitled "How to Get a Head in Navigating", which the Cannibals believe they can use to replace the Head. The second time they help Guybrush by preparing a Voodoo Antiroot that dissolves ghosts.
The Curse of Monkey Island
In the third game the cannibals have relocated to Blood Island where they now worship the island's volcano god, Sherman, and a new pantheon of food-related gods. They apparently moved to get away from LeChuck's amusement park.
The three cannibals seen in this game are Lemon Head, Pineapple Head and Banana Head. The cannibals have now also completely abandoned their cannibalistic nature and consume only tofu, vegetables and fruit. This reflects their new attitude as Sherman is easily irritated by other foods such as meat and is highly lactose intolerant. As such, instead of human sacrifices, the cannibals offer human mannequins made of fruit.
In this game Guybrush has to dupe the cannibals into believing he is an ambassador of another Cannibal tribe in order to get to the crater to witness the cannibals' ceremony and dump some cheese into the volcano in order to cause an eruption.
Of the three original cannibals only Lemon Head returns in the third game, but slightly altered. Whereas the cannibals in the first game were all extremely muscular Lemon Head has become quite thin. This may have been due to a change in diet, or is simply the decidedly heavy shift in art style between the first two games and the third. Additionally, whereas in the first game Lemon Head was a quiet figure who followed the lead of Red Skull, in the third game he has become the leader of the cannibals and is more verbal, but still very mellow with a very erudite method of speaking. His name is spelled Lemonhead in the game's subtitles.
He is the only cannibal with a known penchant for arts and crafts, as evidenced by the Tiny Idol found near the Great Monkey Head. He is also notably gullible, not realising the Tiny Idol was something he made even after seeing his signature on it. He also did not recognize the supposed Cannibal diplomat as Guybrush even though his disguise was simply a carved block of tofu over his head, with his clothes remaining the exact same.
Red Skull and Sharptooth
Red Skull is the most vocal of the three Cannibals of Monkey Island and seems to act as a spokesman. He is also the biggest proponent of getting out of the cannibal lifestyle, citing concern for everyone's arteries. Sharp Tooth, meanwhile, is the biggest advocate of sticking with their traditional cannibal lifestyle. He is fond of root beer floats.
It is unknown what happens to Red Skull and Sharp Tooth after the first game. While it is possible that they might be Pineapple Head and Banana Head, it is not out of the question that the differing lifestyles led the cannibals to go their separate ways. Their subsequent residence is unknown.
In The Secret of Monkey Island: Special Edition Sharptooth is voiced by Patrick Hallahan; Red Skull, by S. Scott Bullock.
It should be noted that the Cannibals are mentioned twice in Tales of Monkey Island: once in "Lair of the Leviathan", when Guybrush asks Morgan LeFlay what to do after he gets a male manatee to stand his ground and thinks of teaching him "the courting dance of the Monkey Island™ cannibals"; and once in "The Trial and Execution of Guybrush Threepwood", when the human LeChuck tells Guybrush his (made-up) story about how he got to Flotsam Island, which involves getting "washed up on an island of cannibals, from whom I deftly escaped using many of the selfsame skills you taught me back on the Jerkbait Islands," to which Guybrush replies, "It's amazing how easily man-eating tribes can be reasoned with."