The planned third evolution of Raichu was called Gorochu.
During the development of the original Pokémon games, Pikachu was designed as part of an evolutionary line. The intended line was Pikachu, Raichu, and Gorochu, with Gorochu imagined as a more powerful final evolution featuring prominent fangs and horns.
Gorochu was removed before release because of cartridge-space limitations. As a result, the original games ended Pikachu’s line at Raichu. The unused name and concept later became known through developer interviews and historical material about Pokémon’s early design.
Pichu is a different character and should not be confused with Gorochu. Pichu was introduced later as Pikachu’s pre-evolution in Pokémon Gold and Silver, completing a three-stage line in the opposite direction: Pichu, Pikachu, and Raichu.