As only three members are ever seen in-game, the species of all Forty Thieves is unknown. The appearance of the three known members changes greatly from animated cutscenes to in-game.
In the cutscenes, they appear to have dark blue fur, red eyes, and a curly goatee. Their snouts are long and sharp, making them look rather canine. They are also tall and wear more clothes: tan clothes with a golden chestplate, and a turban with a circular turquoise stone in the middle of it. They use scimitars as weapon of choice.
In-game, their fur is brown and light-yellow. Their noses are round and red and they also have visible rodent teeth and whiskers. Their eyes are white with blue irises, and their ears are visible under the turban, that is also the only clothing they wear.
- The gang's name is an obvious reference to the story of Ali Baba and the Forty Thieves from the Arabian folktales One Thousand and One Nights.
- The thieves rescued in-game all have feline-themed names, despite all of them being mice.
- The thieves seen in the animated cutscenes planning with Salim are probably The Lion, the Panther, and the Tiger.
- According to Sly, most of the Forty Thieves retired long before he and the gang arrived. This is much different than the thieves in the story of Ali Baba, in which they all die.