He is proud and vain - He invents elaborate ceremonies in honour of himself. He struts about the farm, putting on airs and hoping all the animals will notice his natural superiority.
He is jealous and touchy (easily offended)by nature - He gets offended when Snowball gets more praise than he does and when he gets drunk from whiskey (as if it were somebody else's fault).
He is scheming and manipulative - Early on in the story he takes Bluebell's puppies to turn them into killer dogs at his beck and call, and he invents lies against Snowball as well as having the dogs chase him away.
He is selfish and uncaring for others - Along with his elitist group, he keeps extra portions of milk and apples and even sells Boxer in the end to the knacker in exchange for whiskey.
He knows his limits - Aware that he lacks skills in oration, Napoleon sends Squealer to speak in his place. He also bides his time until the puppies grow up and are trained to be the secret police he needs before trying to repress the animals by force.