Vegeta is a very strong Saiyan. He was prince of the planet Vegeta. At first he was evil, but later he became good. He was forcefully taken by Frieza. Frieza and King Vegeta were working with each other. Frieza wanted to have King Vegeta's son and he allowed him. Frieza made Vegeta the way he is now: cold hearted and evil. He had no other choice. Frieza made Vegeta do what he wanted or else Frieza would kill his father. Even though Vegeta did, Frieza still killed him when they tried to rebel against him.
Then Vegeta turned on Frieza and went his own way. He always hated Frieza especially after he destroyed the planet which killed his father, and how Frieza made him act the way he does. Vegeta, Nappa, and Raditz all worked for Frieza and Frieza thought that they were weak. Vegeta knew all along that his planet was destroyed by Frieza, but he acted calm and he knew that fighting a lot and taking over planets would make him stronger and they then he would get his revenge on Frieza.
After Raditz was killed, Vegeta and Nappa heard that there were Dragonballs on earth, so they went there to make a wish. They thought it would be easy, but the earthlings prepared themselves for the battle, and the Saiyans thought that Gokou was going to be easily defeated by Nappa. Then finally he came and Gokou's power level was much higher than it was a year ago. Even though Gokou was much stronger, Vegeta was still a challenge for Gokou. Vegeta made an artificial moon and turned into a giant monkey. They cut off his tail and Gokou hit him with a Spirit Bomb, but since Vegeta hit him first the Spirit Bomb lost some power and Vegeta survived it. He went back to the planet Frieza and they cured him quickly, but he escaped to get the Dragonballs on Namek.
On Namek, Vegeta defeated all of Frieza's henchmen. When the Ginyu Force came, he killed Goldo, but lost to Recoome. Then Gokou came. He could tell that Gokou was the legendary Super Saiyan!!! After Gokou healed him, Gokou killed Recoome and Vegeta killed the other two members, Burter and Jeice. But he had trouble fighting Frieza. Vegeta had gained a lot of power from fighting, but was he strong enough to kill Frieza? Vegeta made Frieza transform. His power was nearly equal. Then into the second transformation. Gohan and Piccolo did most of the attacking. Then the third and fourth. While waiting for the fourth, he asked Klilyn to beat him up and nearly kill him. If he did this, then he could get to a whole new level of power and become much stronger. He even thought that he could even become a Super Saiyan. In the fourth transformation, however, Vegeta was easily defeated by Frieza. His powers were quick enough to see the fast fireballs of Frieza, but he wasn't strong enough. Then when Gokou came to help, Vegeta had a breakthrough. While laying on the ground nearly dead happy to see Frieza's match, he explained to Gokou why he had to defeat him. Then Vegeta started to cry and died. Vegeta was really good at heart, but had no choice but to act like how he did.
Vegeta was very cocky. He knew that even if he lost a battle that he would grow stronger because a Saiyan that loses, gets stronger all the way to their peak in strength. He also trained hard like Gokou to be very strong. His training to become the strongest started because he couldn't accept being defeated by a low class Saiyan (Gokou), then seeing Gokou transform into a Super Saiyan. He copied Gokou's training to become Super Saiyan, by training in 400 times gravity!!!! He became very strong. But even though he did a lot of training and fighting, and was a high class soldier and prince of the Saiyans, he wondered why Gokou was still stronger than him. There were many people that Vegeta couldn't defeat that Gokou could. The reason was because Vegeta didn't have the fighting spirit Gokou had and he didn't have a pure heart. But after Gokou had died in the fight with Cell, Vegeta had lost his will to fight. He missed Gokou and never cared for fighting. Until Gokou came back to fight Majin Buu. While Vegeta was fighting Majin Buu, before he sacrificed his life to try and destroy him, he told Trunks how much he cared about him, since Trunks was his son. This is when Vegeta finally becomes a true good guy.
He watched Goku defeat Majin Buu and he realized that the pure heart that Gokou had was the reason why he always won.
Vegeta marries Bulma and has 2 kids: Trunks and Bra.