Son Goku
Son Goku is the primary hero of the Dragon Ball series. The series started out with Goku as a child of age 12. Once he grew up and his son was born, the TV series' name changed from Dragonball to Dragonball Z. At the end of the series, Goku was roughly 45 years old.

Goku is a Saiyajin whose native world is the planet Vegita. He was sent to Earth in a space capsule right after he was born so he could conquer the planet. However, he hit his head and lost his "programming," thus becoming the kinder, gentler Goku we see in the series. Goku was raised as a human on Earth, and did not learn of his true nature until his brother Radits came to Earth...
Later, when Goku's rage was awakened by witnessing the death of his friend Krillin, his Super Saiyajin power was awakened. When he goes Super-Saiyajin his eyes turn green and his hair gold. Currently, Goku can go to the 3rd stage of Super-Saiyajin power.     

Son Gohan
Son Gohan is Goku's first son. At the end of the series he was 26 years old.  For a short while after the second time Goku died in the series, Gohan became the primary character. Gohan is the most powerful non-fused character in the DBZ world, but lacks the love of fighting his father has and thus rarely uses his full strength.

Gohan is a very good-natured boy and unlike his father, hates fighting, although for a while he was more powerful. He is very polite towards just about everyone except to his enemies, and when he's ticked off. Gohan is very bright and studies very hard, although this is somewhat due to the wishes of his very strict mother...
Gohan is the first character in the series to have gone Super Saiyajin-2, during the Cell Game; the power of his anger was kindled by watching his friends get beaten up, and the death of Artificial Human #16 sent him over the edge. It was roughly at this time that the series switched main characters from Goku to Gohan.

Piccolo
Piccolo is Goku's old rival. He was born after Goku killed his father when he was a kid; in his last breath the old Piccolo spat out an egg, and the new Piccolo hatched. Piccolo then went on to fight Goku in the final round of the Tenkaichi-Budokai, which he subsequently lost by a very close margin.

Piccolo is a native of the planet Nameck, although he doesn't learn this for quite some time after his first appearance. As a Nameck, he can regenerate almost any part of his body lost. (usually the arms) He can also extend the range of his arms till they're really long. Later, he goes to Nameck to help Kulilin, Goku, Gohan, and Vegita fight Freezer.
After the Tenkaichi-Budokai, Piccolo becomes more and more of a "good guy." Eventually he becomes Goku's friend; fairly recently he got ticked off at Trunks and gotenks for calling Goku weak. Once one of the most powerful characters in the series, he has sort of reached a "middle ground," neither weak nor strong among the Z fighters.

Vegita
Vegita is the "bad guy among the good guys." He first made his appearance back when Gohan was 4. Although he fights alongside the other Z fighters, he is still decidedly evil. As the prince of the Saiyajins, he is very proud, has a huge ego, and is constantly trying to prove that he is the best fighter in the universe.

Vegita has a continual rivalry with Goku, or "Kakarott," (Goku's Saiyajin name) and is obsessed with beating him in combat just to show that he is the stronger. This obsession with trying to be stronger than Goku proves to be a fairly large weakness as well.
Despites his efforts to show otherwise, Vegita has changed and has developed a conscience, and deep down cares about his friends. Furthermore, he is also somewhat emotional at heart. He demonstrates this when dealing with his son Trunks, most notably just before he died trying to kill Majin-Buu. Although he pretends to hate Goku with a passion in reality he respects his power and maybe even likes him a bit.                        Next page