Gyarados first appeared in Beauty is Skin Deep where it was used to protect Clair's Dragonair while it was a Dratini. Thinking that Dratini was under threat, Gyarados attacked Ash, Misty and Brock but stopped when Clair realised that they meant no harm.
Gyarados was a powerful fighter and was used in Clair's second Gym battle with Ash. It defeated Ash's Snorlax by paralyzing it with DragonBreath and finishing it with Hyper Beam. It also put up a good fight against Pikachu but was eventually defeated by the electric Pokemon.