It is not known to evolve into or from any other Pokémon.
Along with Entei and Suicune, it is one of the Legendary beasts resurrected by Ho-Oh after the burning of the Brass Tower. Of the three Legendary beasts, Raikou is said to represent the lightning strike which ignited the fire that consumed the Brass Tower.
This section temporarily contains information copied directly from Bulbapedia, and needs to be rewritten so not to be classified as plagiarism.
Raikou is a quadruped, yellow, tiger-like Pokémon with black stripes and a white underside. It has a thin, light blue tail with sharp angles and a spark-shaped formation at the end. Most of its face consists of thick, white fur and shorter yellow fur around its red eyes. Raikou's muzzle is a light blue "X" and it has a black faceplate with two bumps that covers its forehead, nose, and ears. Raikou has two long fangs that make its appearance similar to the saber-toothed cat. Its large claws each converge to form a single point and never retract. Extra fur hangs off its body in front of its thighs. Raikou has a mane across its back that resembles dull purple rain clouds and allows it to shoot bolts of lighting.
As seen in the anime, Raikou is able to fly by creating storm clouds. It is shown to be distrustful of humans, though it may form some friendship with those who help it. Raikou tends to appear during thunderstorms and when other Electric-type Pokémon are in danger. Raikou races across grasslands while barking cries that sound like thunder.