Sharptooth is a villain in Erin Hunter's Warriors book series. He is a savage mountain lion who preys on smaller cats and serves as the main antagonist of Moonrise, the second book of the story arc The New Prophecy.
Sharptooth is mentioned to be a giant cat; a mountain lion, living in a cave near the Tribe of Rushing Water, preying on the Tribe cats. He is greatly feared by the Tribe, and guards are assigned to go with hunting groups to watch out for him.
Stoneteller receives a prophecy that a silver cat would come and save them from Sharptooth. He tells this to the Tribe, saying that all they can do is wait for the silver cat to arrive, and to not lose hope.
When Brambleclaw, Squirrelpaw, Stormfur, Tawnypelt, Crowpaw, and Feathertail arrive at the Tribe's home, they realize that the Tribe seems to be afraid of something, which is later confirmed to be Sharptooth after Stormfur sights the mountain lion. The Clan cats, eager to return home, attempt to leave, but Stoneteller tells them that Stormfur can't, because he is prophesied to defeat Sharptooth. The other Clan cats try to help Stormfur escape, but Sharptooth enters the cave, allowing them to rescue him during the commotion. As they leave with Stormfur, they see Sharptooth leaving with Star in his jaws.
While the Clan cats are on the run, they get lost and enter a cave, stumbling upon Bird, Rock, and Talon, who are former Tribe cats. The three loners tell the Clan cats how the Tribe of Endless Hunting chose six cats, including themselves, to go and kill Sharptooth. They failed, and three cats were killed, leaving just Bird, Rock, and Talon. However, the surviving cats could not go back to the Tribe while Sharptooth was still alive, because it was the will of their ancestors for them to defeat him, so they now live as loners in a cave. Stormfur, who is now starting to think that he in fact is the silver cat, knows he must return to the Tribe and kill Sharptooth, which they all agree on. When they wonder how to kill him, Squirrelpaw says that if they themselves can't kill Sharptooth, then something else can.
The Clan cats return to the Tribe, and it is revealed that Sharptooth killed two cats and severely injured two others. Talon, Rock, and Bird also return, saying they want to help, which Stoneteller allows. Squirrelpaw says that the plan is to stuff a dead hare with deathberries for Sharptooth to eat, and they all start preparing. While the Clan cats stuff the hare, Talon cuts his paw to leave a blood trail as bait. Sharptooth follows the trail and comes, however, he doesn't eat the hare and instead goes for the cats. Squirrelpaw, coming out of hiding, tries to distract him, but Sharptooth goes for Crowpaw, who couldn't hide in time. Seeing this, Feathertail reveals to Stormfur that she is the silver cat, as she has heard voices saying this is for her to do. She leaps up to the roof of the cave, sending stalactites down on the mountain lion, killing him instantly, though also dying in the process. The Clan cats mourn her while the Tribe celebrates Sharptooth's death.
Sharptooth is mentioned a few times in later books.
Sharptooth on the Warriors Wiki
The Dark Forest