The Red Gyarados is a shiny Pokemon that is red in appearence instead of blue which is the colour for normal Gyarados.
The Red Gyarados appears in both the Pokemon games and in the Anime.
In both the games and the Anime, the Red Gyarados was at first enraged and out of control due to its forced evolution thanks to Team Rocket, however it calms down once captured.
In Pokemon games Silver, Gold and their remakes the Red Gyarados is an event Pokemon which can be captured at the Lake of Rage.
It was forced to evolve as a Magikarp by Team Rocket using radio waves. This made it very angry and the player would have to catch it to calm it down.
The Red Gyarados is also mention in Pokemon Diamond and Pearl at the start of the game in a news flash.
The red Gyarados's first appearance in the Anime was in "Talkin' 'Bout an Evolution" where it leaped out of the Lake of Rage and fired a Hydro Pump at Ash and his friends.
Team Rocket would try to capture the shiny Pokemon. Under the command of Team Rocket member Tyson, three Rocket field agents: Jessie, James and Meowth try to capture Gyrados but other Team Rocket members capture it with a special made net.
After Team Rocket's success in catching the red Gyarados, they decide to do some research on it. Meanwhile, Lance a Dragon trainer, finds out that the Evolution Inducement Ray was the cause of all the unevolved Pokémon growing tired. He then destroys it by with the help of Dragonite's Hyper Beam. After the machine was destroyed, all of the side effects it caused disappeared. No longer affected by the ray, the red Gyarados begins to go on a rampage. It then escapes from the helicopters Team Rocket was carrying it in and dives into the water below. The red Gyarados continues the rampage, destroying everything in sight with Hyper Beam. Ash tries to stop it from going berserk, but it had no effect, making Gyarados retaliate with Hydro Pump. The Team Rocket grunts shoot the same net as the one from the previous episode. This time, Ash sends out Bayleef to cut the net with Razor Leaf. Just when the grunts are defeated, the Team Rocket trio arrive and shoot a different net at the red Gyarados. Gyarados breaks free from the net and goes on another rampage, moving towards the river in Mahogany Town. Pryce stops the Atrocious Pokémon from going any further by having his Dewgong use Ice Beam on the river. Lance, after defeating Tyson, battles the red Gyarados with his Dragonite in order for it to calm down. Lance successfully does so and catches the red Gyarados.