Before being an ally of Goku and the other Z Fighters, Vegeta was a villain who already killed several people in Dragon Ball Z. His version known as Majin Vegeta killed innocent people without remorse, and Dragon Ball GT showed that this killing was very worse than it looks.
The Shadow Dragon from Dragon Ball GT was born from the slaying of Majin Vegeta
In episode 52 of Dragon Ball GT, Goku and his friends wanted to ask Shenron to restore peace to the world, but the Dragon Balls were possessed by negative energy.
Unaware of this, the characters gathered the spheres and gave rise to the Seven Dragons of Shadows. Originally, a Shadow Dragon was born from the request that was made because of Vegeta.
In the last saga of Dragon Ball Z, Vegeta let Babidi control his mind so he could finally have his revenge against Goku. Thus, he became Majin Vegeta to gain more power. To convince Goku to fight him, Vegeta killed hundreds of innocent people, who were watching the Martial Arts Tournament.
The aftermath of Vegeta’s attack
Before being possessed by Babidi, Vegeta had already become a good person and lived in peace with his family. However, he wanted to go back to being the proud warrior he was before living on Earth. So he accepted to become a darker person to defeat Goku and prove that he is the strongest.
Eventually, the dead people came back to life with the Dragon Balls and Vegeta redeemed himself for his mistakes. However, Dragon Ball GT confirms that this wish had the consequence of creating one of the Shadow Dragons. This small detail shows that the killing of Majin Vegeta did more damage than it seems.