Goku’s origin story in Dragon Ball already had much in common with Superman, but Dragon Ball Super: Broly brings the two backstories even closer.
Dragon Ball Super: Broly made some alterations to Goku’s established backstory, bringing his origin even closer to that of Superman. Even before the release of Dragon Ball Super: Broly, Goku and Superman had much in common. The Saiyan warrior known as Kakarot came to Earth from a distant planet on the verge of destruction and, as the last of his kind, combines the best of his own heritage with the principles of a human upbringing to become the God-like protector of Earth.
Similarly, Superman came from Krypton as Kal-El during infancy, leaving behind a planet in ruins, and was inspired by his caring adoptive parents to use his otherworldly abilities for the good of mankind. The key difference in Goku’s origin story, as established in Dragon Ball and Dragon Ball Z, is that while Superman’s parents sent him to Earth because they had advance knowledge of Krypton’s impending destruction and wanted to save their son’s life, Goku’s father was largely uncaring about his distinctly under-powered son and Goku was actually sent to Earth to conquer the planet.
The most recent Dragon Ball cinematic release, Dragon Ball Super: Broly, partly retcons this version of events. Instead, Goku is sent to Earth as a slightly older child, wearing a suit of Saiyan armor, instead of arriving as a baby. More significantly, Dragon Ball Super: Broly establishes that Goku was not actually meant to clear Earth of its inhabitants, but was sent by his parents after Goku’s father, Bardock, became suspicious that Frieza might destroy the planet Vegeta. This story changes the established characterization of Bardock from a typical Saiyan who had no emotional attachment to his son, to a father who would sacrifice his own life to save that of his children.
Dragon Ball Super: Broly’s changes take away the one key difference between Goku and Superman’s origin stories. Now, both characters went sent to Earth by their smart and caring biological parents to save them from the destruction of their respective home planets.
Akira Toriyama, creator of the Dragon Ball franchise, has developed somewhat of a reputation for rewriting Dragon Ball canon – particularly with the recent Dragon Ball Super material – and these changes have mostly been criticized by fans, including the latest alteration to Goku’s origin. The rewrite doesn’t add anything to the story of Dragon Ball Super: Broly that couldn’t have been worked into Goku’s established history and it could even be argued that the new version takes away from certain other elements of the character.
For example, Grandpa Gohan was instrumental in Goku developing his keen sense of morality after a bump to the head cleared out his Saiyan aggression. However, painting Bardock as a more caring parent suggests that Goku was inherently more kind and just than the average Saiyan, taking away from the influence Grandpa Gohan had upon the child. The sequel to Dragon Ball Super: Broly is sure to make even more adjustments to what fans already know about the franchise, but hopefully they won’t involve developing X-ray vision or the arrival of Goku’s biological female cousin.