Raikou belongs to a trio of legendary pokemon, the other two being Entei and Suicune.
Raikou is said to be the embodiment of lightning/thunder, and unlike Entei and Suicune, is not in his own movie, though he does have a one hour special episode called "Raikou: The Legend of Thunder!"
Raikou also has a Giant Pokemon Center edition Plush, along with the other two beasts.
Raikou is available to catch in pokemon Colosseum (from the third boss, Ein) and in fire red and leaf green, when you pick Squirtle as your starter and beat the elite four. (appears at random)
Also one of the best pokemon out there.
Liz: That's a big stuffed animal Tom, it's not real get over it.
2. "A wild Raikou appeared!"
Liz:WOAH a thunder tiger!
3. Raikou, one of the three legendary beasts of the second generation.