Goku, known originally as Kakarot, is the central protagonist of Dragon Ball Z Kai. His background reveals a dramatic origin: he is a Saiyan, a powerful warrior race, who was sent to Earth as a baby with the mission to conquer the planet. This violent purpose is entirely erased after he suffers a severe head injury shortly after arriving, which rewrites his aggressive programming and allows him to grow up as a kind-hearted and innocent boy in the wilderness, raised by his adoptive grandfather.

As an adult, Goku’s personality is a unique blend of childlike naivete and pure-hearted bravery. He is fundamentally cheerful, optimistic, and often oblivious to social norms and formalities. While he appears to be a simple-minded bumpkin with a lack of common sense, this belies an incredible genius for martial arts and combat strategy. In Dragon Ball Z Kai, his characterization is notably more faithful to the original manga, revealing a more nuanced and self-interested motivation. Unlike the more traditionally heroic portrayal in some versions of the anime, this Goku is driven less by altruism and more by a deep-seated Saiyan desire to fight and overcome powerful opponents. His compassion and mercy are often extended to his enemies not solely for their redemption, but because he envisions a future rematch and sees killing a worthy adversary as a waste.

His primary motivation is the endless pursuit of self-improvement and the thrill of challenging battles. While he deeply loves his family and friends, his passion for fighting frequently takes precedence, leading him to be somewhat neglectful of his domestic life. His role in the story is that of Earth’s ultimate defender, the one who must repeatedly rise to face increasingly cosmic threats that no other fighter can handle. This position often forces his companions into the role of spectators, praying for his success as the fate of the world rests on his shoulders.

Key relationships define his journey. His rivalry with Vegeta is central, acting as a reflection of two paths a Saiyan can take; where Vegeta is prideful, cruel, and driven by a desire for conquest, Goku is humble and compassionate, yet both share an insatiable hunger for strength. He has a profound bond with his son, Gohan, whose hidden potential often serves as a reminder of Goku's own dual Saiyan-human nature. He also forms a crucial student-teacher relationship with King Kai, the North Kai of the universe, who mentors Goku in the afterlife, teaching him powerful techniques like the Spirit Bomb and the Kaioken, and helping him unlock his latent Saiyan power through rigorous and eccentric training.

Over the course of Dragon Ball Z Kai, Goku develops from a powerful but unknown fighter into the legendary Super Saiyan, a transformation that represents the pinnacle of his warrior race, awakened by righteous fury and the pain of losing a loved one. His development is a constant cycle of sacrifice, death, and rebirth, as he continuously pushes past his limits to protect his loved ones. However, this growth is often a double-edged sword; his eagerness to test his power and let his enemies reach their full potential can put the entire universe at risk, showcasing a reckless and selfish side to his heroic nature.

His notable abilities are legendary, including the iconic Kamehameha wave, a concentrated energy attack he learned from his master, Master Roshi. He also masters the Kaioken, a technique that multiplies his power at great risk to his body, and the Spirit Bomb, a desperate last-resort attack that gathers energy from all living things. As the series progresses, he achieves the legendary Super Saiyan form, vastly amplifying his combat power and marking him as one of the strongest beings in the universe.