Rhydon is widely credited as the first Pokémon designed during development of the original games.
Rhydon was created by Ken Sugimori, the artist responsible for much of the original Pokémon artwork. Its early design reflects the series’ initial focus on battling monsters, with a large dinosaur-like body, a horn, and powerful physical features.
Although Rhydon has National Pokédex number 112, its low number does not indicate when it was designed. Early concept development and final Pokédex ordering were separate processes. Rhydon’s design is also associated with early Game Freak development materials and has long been identified as the first Pokémon created.
Pikachu is often guessed because it became the franchise mascot, while Mew is sometimes guessed because it was added late and has Pokédex number 151. Neither is generally credited as the first design.