The Three are three cats who are destinied to save the clans from the Dark Forest and final battle. The Prophecies around them are, There will three, kin of you kin, who hold the power of the stars in their paws. After the sharp-eyed jay, and roaring lion, peace will come on dove's gentle wing. And, the end of the stars draws near, three must become four to battle the darkness that lasts forever. The tree are all reincarnations of cats from the ancients. It was revealed later that the Three kept their powers after the Final Battle.
Lionblaze is one of the three. His power is that he can't be injured or killed in battle, he is also very strong and can take on a whole patrol of cats single pawed. His ancient counterpart is Lion's Roar.
Jayfeather is one of the three. His power is that he can walk into cat's dreams and read their minds. Since he is blind, he can see in dreams. His ancient counterpart is Jay's Wing.
Dovewing is one of the three. Her power is that she can hear things very, very far away and get a generarl image of it in her mind, once her powers were temporarily blocked but later returned. Her ancient counterpart is Dove's Wing.
Originally, Jayfeather and Lionblaze thought that Hollyleaf was the other one of the three because she is their sister but later it was revealed that she isn't. She doesn't have any powers or an ancient counterpart.
Jayfeather recieved a prophecy saying, ".....three must become four....." meaning that there must be four cats, the fourth cat is later revealed to be Firestar