Goku

Goku is the main character of Dragon Ball Z. He is a Saiyan who was originally sent to Earth when he was an infant to kill everybody. However, he fell down a cliff and hit his head and didn't remember anything, and was taken in by a human named Gohan. Now he defends Earth. He married Chichi and had two sons, Gohan and Goten. He didn't know he was a Saiyan until he was told by Radditz in the beginning of Dragon Ball Z, and that his real name is Kakarot. Even though he is a 3rd class Saiyan he is usually the strongest character for most of Dragon Ball Z, even more powerful than Vegeta who is the prince of the Saiyans. Goku got his tail surgically removed when he was a baby so the light of a full moon no longer turns him into an Oozaru.

Gohan

Gohan is Goku and Chichi's first child, he is only half Saiyan unlike his father but because he started fighting at an early age he becomes one of the strongest characters throughout Dragon Ball Z. He was first trained by Piccolo and he has always looked up to him. He was also the first to go Super Saiyan level 2, and played a crucial role in defeating Cell. Gohan got him name from Goku's foster-dad, Gohan, who took care of Goku when he first landed on Earth.

Vegeta

The mighty prince of the Saiyans. He was a bad guy early in the series but was forced to join the Z warriors on Namek to fight against a stronger opponent, and then sides with them after that. He has a kid with Bulma named Trunks. He is the second to go Super Saiyan and is always trying to out do Goku. Even though he fights with the good guys he is still a bad guy with an evil heart until he does a suicide attack as Majin Vegeta attempting to save the planet.

Piccolo

Piccolo is a Namekian. He is Kami's evil half, if either of them die they will both die. In the very begining of Dragon Ball Z he is an enemy of Goku. However, when Radditz arrives he joins up with Goku and together they kill Radditz. Afterwards he takes Gohan away to train him and he becomes friends with him. Then Piccolo is a good guy from that point on.

Krillin

Krillin is Goku's best friend. He is with him from the beginning. When he dies in the battle against Freeza it triggers Goku's anger and turns Goku into a Super Saiyan for the first time. Krillin used to be a monk so that is why he has six dots on his head. He does actually grow hair later in the series, and marries Android 18 and has a daughter.

Future Trunks

Trunks is the son of Vegeta and Bulma. In the future, him and Gohan are the only survivors of the Android's attack. His mother, Bulma, builds him a time machine which he uses to go back in time. When he first appears from the future nobody knew he was Vegeta and Bulma's son except for Goku and Piccolo. (He told Goku and Piccolo over heard). He is very powerful (almost as powerful as Goku at that time), and defeats Freeza and King Cold before Goku arrives back on Earth. He then helps with fighting the Androids and Cell, then travels back to the future. Back in his time, he is able to easily defeat the Androids because of the training he got with Vegeta in the hyperbolic time chamber (which was destroyed in his future time).

Trunks

Trunks is Goten's best friend. He is always one step ahead of Goten though, being a year older. He is the first to do the Fusion dance successfully with Goten, transforming into Gotenks.

Tien

Tien has three eye's on his head but is still considered an Earthling because that's where he was raised. His best friend is Chou Zu. He is a pretty good fighter, he's a little stronger than Yamcha. In Dragonball he was Goku's enemy and was even more powerful than him, but Goku eventually beat him after Tien used up his energy fighting Piccolo Diamaou. He appears in DB and DBZ but isn't in DBGT.

Yamcha

Yamcha used to be a bandit and robbed people, but eventually became Goku's friend when he learned about the Dragon Balls. He was Bulma's boyfriend early in the series up to about a 1/3 through DBZ, then Bulma started to like Vegeta. Yamcha plays Baseball to earn money.

Chauzu

Chauzu is a prince from another planet and is Tien's best friend. His origin is unknown to anyone but himself and Tien so nobody knows what planet he's from. He is relatively weak and small, so he doesn't put up much of a fight.