Many fans of the Dragon Ball franchise think that the Prince of Saiyans, Vegeta, should be at least as important as the actual protagonist, Goku. However, there is one scene close to the end of Dragon Ball Z that is so perfect that it should just have been the conclusion of the manga, and it also proves why Vegeta will never be the real protagonist of the series.
Vegeta made his debut in Dragon Ball Z as an incredibly powerful and cruel villain who perfectly showcased the best and worst qualities of the Saiyan race: strength, pride, but also a sadistic enjoyment of violence. Goku, who is a Saiyan who grew up on Earth after losing his memory, was barely able to repel Vegeta's attack and survive. After that first encounter, however, a gap in strength developed between the two, with Vegeta forced to play second fiddle to Goku even after he abandoned his villainous ways, redeemed himself, and became one of Earth's protectors. Vegeta's character development is one of the most compelling features of Dragon Ball Z, and it reaches its perfect conclusion at the end of the Majin Buu Saga.
Related: Dragon Ball Super Finally Teaches Goku What It's Like to be Vegeta
The powerful demon Majin Buu became a threat to Earth and the entire universe after being unleashed by the evil wizard Babidi. None of the Z warriors were strong enough to stop him, and they were all taken out one by one until the duty of stopping him rested entirely on the shoulders of Goku and Vegeta (with some unexpected but essential help from Mr. Satan). In Dragon Ball chapter #516, Goku finally kills Buu using a Spirit Bomb, following a plan concocted by Vegeta. When the threat is over, Goku and Vegeta share a rare moment of camaraderie, with a rare smile from the Prince of Saiyans and the now-iconic thumbs-up gesture from Goku. The anime made this scene even better, showing the two exhausted Saiyans giving each other the thumbs up, with Vegeta lying on the ground and Goku standing over him.
This is simply one of the best scenes in Dragon Ball, and it's so perfect that if the manga ended right there no one would have complained. Shortly before, Vegeta had an emotional monologue where Vegeta finally admitted that he can never surpass Goku, which was the crowning moment of his whole character development. It also proves that, despite how popular he can be, Vegeta will never be the protagonist of Dragon Ball, because that title belongs to Goku. It's the "gentle Saiyan who still loves to fight" who saved Vegeta, sparing his life when he first attacked Earth, because he knew that even the evilest villain still deserves a chance at redemption. Goku did the same with all his opponents, even Frieza and Majin Buu, because that's just who he is. Without Goku, Vegeta would never find the motivation to grow and better himself, not only in terms of strength but also as a person.
For these reasons, the conclusion of the battle against Majin Buu is not just Vegeta's best moment, but Dragon Ball's best moment too as it showcases the relationship between the series' two main characters, using just Goku's simple gesture and Vegeta's snarky comment. It also highlights the role that each one had in the manga, proving that Vegeta's redemption could have never happened without Goku, who is thus Dragon Ball's one and only protagonist.