Rhydon was the first Pokémon created by Game Freak.
Rhydon is a Ground- and Rock-type Pokémon introduced in the first generation. It evolves from Rhyhorn and can later evolve into Rhyperior when traded while holding a Protector, a feature added in later games.
Its early creation predates the finished Pokémon Red and Green games. Rhydon’s sprite and design were important enough that it appears in several early Pokémon development references and in the original games’ internal data. This does not mean Rhydon was the first Pokémon shown to the public, nor that it was the first one encountered by players.
Rhydon is also notable for its place in the Pokédex: it is numbered 112 in the National Pokédex, while its pre-evolution Rhyhorn is 111. Fans sometimes confuse “first created” with “first in Pokédex order”; the two facts refer to different milestones.