The Fossas are the main antagonists of DreamWorks' 10th full-length feature film Madagascar (despite their role being small), and the secondary antagonists of All Hail King Julien.
They were voiced by Fred Tatasciore and Tom McGrath (who served as one of the directors of the film, the latter also being the voice of Skipper).
Although they are the main villains, they have little screen time. The fossas first appeared when they crashed King Julien's party and attempted to eat Mort, but when Alex noticed a spider on his back, his scream scared the fossas away.
The fossas made a short appearance during the "What a Wonderful World" scene, where they watched Alex walk through their territory after his predatory instincts forced him to attack his friends.
Then when Marty convinced Alex to go on the ship with them, the fossas appeared once again and attacked Marty, Melman, and Gloria. Private and his fellow penguins came to the three animals aid, and Alex showed up and clobbered the fossas and scared them away once again. After that, the fossas never bothered the lemurs, Alex, and his friends anymore.
Like predatory and carnivorous animals in real life includes their real-life counterparts, fossas love to hunt animals as food. The reason why they proved villainous in film was due to them being more obsessed in hunting lemurs than any other potential preys available and are indifferent with the fact that focusing their hunt for lemurs would made them go extinct.
A real-life fossa
Early models of the Fossas
The Fossas trapping Mort in a salad bowl
The Fossas stepping aside for the wild Alex
The Fossas knocked out by the penguins
The Fossas at the mercy of Alex
Alex fighting the Fossas
Alex lifting his friends in front of the Fossas
The Fossas' defeat
The Fossas as they appear in All Hail King Julien.
Unlike their appearance in the film, in real-life, fossas hunts alone, not in packs.
They are misspelled as "Foosa" in the movie, Netflix original, and video game.
They apparently have their own soveriegn called King Fossa in the videogame, who does not appear in the movie at all. He serves as the final boss and as a playable character in the shuffleboard minigame.
They are commonly mistaken as canines or felines, but they are in fact related to mongooses.