In the Universe, there are Kryptonians, and there are Saiyans. For millennium, these two species lived far from each other, but are aware of each other's existence. But with the destruction of their planets, only one remains of each race. On Krypton, Jor-El sends his son to Earth because its atmosphere and yellow sun can give him powers beyond any being in its natural state; On Vegeta, Kakkarot was sent to Earth in order to cleanse the planet. But neither Jor-El, nor Bardock knew that their sons would eventually become the greatest defenders of the Universe.
35 years later, Goku Kent waited for his brother, well, Kryptonian step-brother Clark Kent, to return from the New York Times newspaper company after several months of hard work. Both brothers realize that the other is not human. He knows that Clark gains strength from the sun of Earth, providing him strength, speed, durability, and reactivity he could only recently catch up to, in addition to heat vision, artic breath and enhanced senses.
He has his Saiyan powers to keep himself in the game; he gets stronger as he fights Clark. Soon enough, in a few days, he will debut as Clark's partner and help to defend the Earth with him.
"Speak of the devil. Look at you, Clark!"
The man himself, known widely as Superman across the world, has been mentoring Goku by taking him on missions protecting humanity for the last two years. Nobody has been able to take him down so far, and as such, Goku aspires to become an inspiration just like him, once he transfers to the Z Fighters on his 35th Birthday.
"I'm back, Goku."