Shift is a talking Narnian ape who was the main antagonist of The Chronicles of Narnia book: The Last Battle.
Shift lived at Cauldron Pool along with Puzzle, a simpleminded talking donkey. Although the two call each other friends, Shift tends to treat Puzzle more like a servant than a friend, constantly manipulating the donkey into doing everything for him. One day, he spots a lion skin floating in the Pool and demands for Puzzle to retrive and wear it. He then uses Puzzle as a pretend Aslan and tells the Narnians that Aslan returned, so that Shift could then subtly rule Narnia through the disguised Puzzle. Eventually he even teamed up with the Carlomenes and their commander Rishda the Tarkaan and later also had help from a cat named Ginger. During this time, he stated that the Calormene god Tash and Aslan were the same, dubbing them Tashlan. He then hands Narnia over to the Calormenes and arranges for the Calormenes to be allowed to cut down several of the talking trees in Narnia (Killing the tree spirits that inhabit them), and reveals that he intends to have most if not all of the Narnians sold into slavery to the Calormenes. His deceit eventually gets a majority of the Narnians killed at Stable Hill in a battle against Tirian, Jill, Eustace and some other loyal Narnians. He met his demise when he was thrown into the Stable by Eustace and was devoured by the Calormene god Tash. Narnia is soon destroyed by the true Aslan and Puzzle and other Narnians including the Pevensies (minus Susan, who is no longer a friend of Narnia) enter Aslan's Country (also called New Narnia).
Shift wanted to take over Narnia by using a fake Aslan (Puzzle) and got everything he wanted. His greediness was what eventually destroyed him. He is interpreted by some to be the Antichrist of Revelation.
The Silver Chair
The Horse and his Boy