The first person to access the Super Saiyan form in the Dragon Ball universe wasn’t Goku – it was a man named Yamoshi. Though never mentioned by name, Yamoshi has been discussed in both Dragon Ball Z and Dragon Ball Super.
Goku had a groundbreaking moment in the Frieza Saga when his anger over Krillin’s death gave him the push he needed to become a Super Saiyan. To those who saw it and the ones who heard about it later, Goku’s powerful transformation came as a huge shock. To the Saiyans, a person achieving such an incredible state was a subject of legends. But once it happened with Goku, it became a goal for others characters as well, including Vegeta. At this point, many Saiyans have been able to access not only this form, but even stronger transformations, such as Super Saiyan 3 and Super Saiyan God.
Goku may have been the first Z-Warrior to go down the Super Saiyan path, but another character from Dragon Ball lore beat him to it centuries ago. The Super Saiyan legend noted by Frieza and Vegeta in Dragon Ball Z was an early indication that Goku didn’t invent the form. Dragon Ball creator Akira Toriyama has confirmed that the character who actually reached this level first was Yamoshi [via Kazenshuu]. According to Toriyama, Yamoshi was a heroic warrior who fought beside five other Saiyans against his people. During his crusade, he accessed the Super Saiyan level, but the power he gained ultimately wasn’t enough. When he lost his life, his spirit was released. Toriyama says that ever since, Yamoshi’s spirit has been on the lookout for six worthy Saiyan heroes to use his power.
Yamoshi’s backstory relates directly to Dragon Ball Super’s Battle of Gods Saga. Apparently, Yamoshi, in a sense, is the Super Saiyan God form. It was his essence that created it. He made a brief appearance during the ritual where Goku gathered five Saiyan souls to help him become a Super Saiyan God and take on Beerus. The silhouette of Yamoshi (revealed to be a Saiyan with a Vegeta-inspired design) can be spotted during the ritual. Later on when Goku was losing to Beerus, Goku revealed that he had spoken to “the Super Saiyan God power”, which urged him not to give up. Goku’s comments suggest that it was Yamoshi himself who communicated this message to him.
The Dragon Ball Z: Battle of Gods movie offered a slightly different take on Yamoshi’s origin story by suggesting that he went through the Super Saiyan God ritual, but these events aren’t part of the show’s continuity since the film’s events were retold as Dragon Ball Super’s first saga, with this particular story being left out of the new version. Instead, most of the official details about Yamoshi stem from Toriyama’s words. Since Yamoshi has only been glimpsed but never discussed at length in the anime, he has continued to be a mysterious figure in the Dragon Ball franchise, and one that fans are hoping to finally learn more about in the second Dragon Ball Super movie.