Raichu has been the forgotten evolution of Pikachu since the days of Pokémon Red & Blue, as it has had to live in the shadow of its more famous earlier self for over twenty years now.
There was a time during the development of Pokémon Red & Blue when Raichu wasn't the only other member of the Pikachu line. A recent interview with three of the principal designers behind the first Pokémon games has revealed that a second evolution for Pikachu was planned at one point.
Ken Sugimori, Koji Nishino, and Atsuko Nishida were interviewed for Yomiuri (in a piece that was translated by Siliconera) about the creation of the first Pokémon games. They talked about the design philosophy behind the original 151 Pokémon and how Nishida was brought on board to design cute monsters that would contrast with the fearsome ones that already existed.
Atsuko Nishida came up with the design for Pikachu based on the specifications of it having to be an Electric-type Pokémon and that it should have two evolutions. Nishida came up with every aspect of Pikachu's design, including the name.
The Pikachu line was originally planned to have another evolution, named Gorochu. The reason behind Gorochu's name is due to the Goro sound being an onomatopoeia in the Japanese language for the rumbling sound of an oncoming storm.
Gorochu's design was intended to be more fearsome than Pikachu's, with it possessing a set of horns and sharp fangs, which would have been a continuation of Raichu's bulkier form.
The design for Gorochu wasn't used due to balance issues surrounding the Pikachu line, rather than any issue with the aesthetic of the Pokémon.
You can also create a Gorochu by fusion a Pikachu and a Machamp together!
Gorochu never left the drawing board and no official artwork of the mythical second evolution of Pikachu was presented during the interview. It didn't take long for the denizens of the Internet to come up with their own ideas of what Gorochu might have looked like.
One of the most impressive pieces came from a Reddit user named u/EmdyOfficial, who came up with their own drawing of what they think Gorochu may have looked like. The original thread can be found here.
A third Pokémon was added to the Pikachu line in Pokémon Gold & Silver, but it turned out to be Pichu, a Baby, who is almost totally useless in every regard. This is even truer for the Super Smash Bros. Melee players out there who remember the annoying baby Pokémon.
The fans have wondered if Game Freak would ever add a new addition to the Pikachu line. The closest we were got so far is the Alolan version of Raichu, which is more of a variant than a true new Pokémon.
We likely won't be seeing a new member of Pikachu's family (except for creepy uncle Mimikyu) for the foreseeable future, so it's nice to take a look into what could have been and envision a world where Pikachu had the potential to become even stronger than it is.