Raikou is a quadrupedal, 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 cover 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 lightning.

A proverb claims that Raikou descended from the sky with a lightning bolt. Raikou is able to fly by creating storm clouds, as depicted in Pokémon Ranger: Guardian Signs. In The Legend of Thunder!, Raikou 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 is said to represent the speed of lightning and can control storm clouds at will. Raikou races across grasslands while barking cries that sound like thunder. Raikou's cries can also send shock waves in the air while shaking the ground at the same time. Raikou loves Raikou Treats made by Snacksworth, who once encountered and raced up a mountain with it in the past. Raging Bolt bears a resemblance to Raikou. According to Occulture, Raging Bolt is believed to be an ancestor of Raikou.

As mentioned in the Sleep Style Dex, while Raikou is sleeping, its breath makes a rumbling sound similar to distant thunder. The moment Raikou awakens, it will quickly travel the lands, with a roar sounding similar to a crashing thunder. Raikou is known to enjoy eating Raikou Biscuits. Raikou can be lured over to a sleeping spot using the Raikou Incense. Raikou has three different sleep styles it sleeps in, they are called Energy-Storing Sleep, Meditative Sleep, and Lightning Sleep.

(Source: Bulbapedia)