Along with Uxie and Mesprit, Azelf is a member of the lake guardians, the Sinnoh region's Psychic-type Legendary Pokémon trio. Azelf is the bringer of willpower.

Azelfs performance is in episodes 78 and 151.

Azelf is a small, gray-blue, fairy-like Pokémon. It has two tails that each have a red jewel on them. These are, presumably, two of the jewels which complement the Red Chain. Azelf has a partially cyan face with another red gem encrusted into its forehead. Azelf has a cone-shaped head with elf ear-like protrusions on each side. Its spirit can leave its body without dying, and can return to the body at will. It can control an individual's will or enter the body of an individual. Legends say that if Azelf is harmed, it can cause humans to lose all will inside of them, making them completely immobile for all eternity. It was shown in "The Needs of the Three!" and "The Battle Finale of Legend!" that it can teleport itself, as well as other Pokémon and humans. Azelf can be very cautious around people and Pokémon. However, if threatened, it will reveal its bold side.

(Source: Pokemon Planet Wikia)