As he appears in Narnia, Aslan is a large, talking lion, who is terrifying, magnificent and beautiful all at once. He appears in different sizes to different people, although he himself never changes; as people grow in wisdom and character, they can perceive more of his greatness. Aslan is very wise, and a powerful force for good, but as Narnians often say, “He’s not a tame lion.” He is dangerous, and an unconquerable enemy, but he is unquestionably good.
Aslan is the one true king of Narnia; all of its inhabitants have faith in him, and obey him absolutely. Generally, he comes to Narnia to aid its leaders and heroes on important missions for external and personal peace, and to protect it from various evils. He watches over Narnia constantly, although he does not choose to solve all of its problems for its inhabitants. Aslan also periodically brings humans from Earth, both to help Narnia, and to teach both peoples important lessons.
Aslan is a divine being, and is therefore very powerful and virtually omnipotent. He possesses a certain omnipresence, and he can manipulate, transport, heal, and manifest himself in different shapes. His breath can heal those who have been petrified in stone, boost the morale of the faithless, and cause sleep for others, like Andrew Ketterley.