When Dragon Ball fans think of a Legendary Super Saiyan, they would assuredly think of Broly as he was the first Legendary Super Saiyan in the wider Dragon Ball universe to go up against Goku and the other Z Fighters. However, in terms of the newly-established canon of Dragon Ball Super, Goku chronologically fought a Legendary Super Saiyan before Broly—and she was just as ferocious.
A Legendary Super Saiyan is a rare member of the Saiyan race who only comes about every thousand years. The Saiyan who inherits this trait may not know what they are until they unwittingly unlock the Legendary Super Saiyan form, but when they do, they become a being that is nearly unstoppable. Not only do they seemingly have an unlimited supply of energy while in their Legendary form, but they also enter a berserker state which leaves them unable to control their actions, leading them to attack and even accidentally kill those closest to them without meaning to.
In Dragon Ball Super Chapter 37 by Akira Toriyama and Toyotarou, Goku and the rest of the Z Fighters have entered into the Tournament of Power, a multiversal battle royale that pitted the ten best fighters from a number of universes to compete against each other for the survival of their realities. During the tournament, a group of Saiyans from another universe, Universe 6, were fighting against Frieza and losing pretty terribly, until one of them discovers that they are a Legendary Super Saiyan–a Saiyan warrior named Kale. After Kale unlocks the god-like power that was always stirring inside of her, she decimates Frieza and then goes on to eliminate nearly half of all the participants in the tournament, and even goes toe-to-toe with Goku amid her ferocious rampage.
While Kale is brought under control by her teammate, Caulifla, her power is proven to be on par with the likes of Broly in this chapter. In fact, fighting Kale and learning that a Legendary Super Saiyan was more than just a legend and could actually exist allowed Goku to be better prepared to deal with Broly as he had some idea of what to expect by the time the two fought in the anime film Dragon Ball Super: Broly.
Even though Broly is perhaps the most iconic Legendary Super Saiyan in the Dragon Ball universe since he was technically introduced first and has starred in four separate movies, Dragon Ball Super reveals that Goku fought a Legendary Super Saiyan before Broly.
