Generation I is where it all began. Players and fans were shocked to learn that the lowly Magikarp evolved into the monstrous Gyarados. It was truly a sight to behold.
As a Water/Flying-type, Gyarados can do some serious damage. It can fit in with nearly any team, whether there is already a Water Pokemon or not. With the right moveset, Gyarados could lead any trainer to the Elite Four.
The best moveset for Gyarados in Pokemon Red and Blue
Almost any Pokemon in Red and Blue that can learn Blizzard should. It can do serious damage against Flying, Grass, Ground, and Dragon Pokemon. Gyarados can put this to good use as those types are pretty common, with Dragon-types being a main part of the endgame.
Thunderbolt is a great coverage move that a lot of Pokemon can learn in Red and Blue. It will take out Water and Flying types with ease, as well as doing some serious damage to other types that may not resist it. A 95 power move with 100% accuracy is too good to pass up.
In Generation I, Body Slam has a 30% chance to paralyze any non-Normal Pokemon. The power behind this move is massive. As a Normal-type move, it can hit a variety of Pokemon pretty hard. Body Slam is often underrated but can be utilized pretty well by a lot of different creatures.
Hyper Beam is the only move in the set that Gyarados learns naturally. That means not by a TM. Hyper Beam does not need to charge up to use, but will require a recharge after use. In Generation I, however, there is a way around this. This incredibly powerful move will not need to recharge if it misses, breaks a Substitute, or if the target Pokemon is knocked out. A one-hit knock-out can keep the Hyper Beam train rolling.