Goku is the hero of Dragon Ball Z, the most powerful warrior on earth and the first to become Super Saiyan in over 1000 years. When the Saiyans arrive, Goku learns the mysterious secret of his own past: He is a Saiyan formerly named Kakarot. Goku was sent to Earth as a baby to grow up and destroy the planet, but a head injury as a child scrambled Goku's programming. Instead of growing up to become a destructive super-warrior, he became innocent and pure of heart, fighting for good. Goku is peaceful, good natured, honest, loving to his family and friends, loyal, trustworthy, brave. If he has a weakness, it is his trusting nature. He always finds the "good" in people when others don't see it, though Goku's enemies sometimes take advantage of his naive trust. He originally trained under Master Roshi and wears his symbol until he trains under King Kai. Then he wears King Kai's symbol. Goku grows up and marries Chi-Chi. Together they have two sons: Gohan and Goten. ATTACKS: KAMEHAMEHA - an energy attack launched with both hands from his side, taught by Master Roshi KAIO-KEN - boosts power level turning Goku red-hot, taught by King Kai SPIRIT BOMB - an enormous attack drawing energy from all living things, taught by King Kai
Named after his adoptive grandfather, Gohan is Goku and Chi-Chi's eldest son. He is idealistic, good and pure like his father. Gohan reveals his tremendous fighting potential when the earth is threatened. His heritage as part Saiyan and part human, make him stronger than if he were of one race alone. With Goku's departure to the next dimension and the eminent arrival of Saiyans stronger than Raditz, Gohan is key to the survival of Earth. Thus Piccolo, a former enemy of his father, joins forces with the good guys and trains Gohan for the upcoming battle. Over time, Gohan becomes friends with Piccolo, looks up to Piccolo and even wears similar clothing. Although initially a wimp, Gohan's training in the wilderness and subsequent fighting make him both brave and loyal. Following the fight on Earth, Gohan is determined to go with Bulma and Krillin to Namek to collect the seven Namekian Dragon Balls and help out his friends on Earth - especially since he feels he let them down during the fight on Earth. Gohan is key to the good guys success on Namek, risking his own life to save Dende, collecting Dragon Balls, travelling to see Guru who awakens a power sleeping within him, battling the Ginyu Force, etc. He will be the first to reach Super Saiyan II stage. 
Goten is the second son of Goku and Chi-Chi, and is Gohan's little brother. Goten loves to train in martial arts. He quickly develops incredibly strong powers (he just naturally goes Super Saiyan) that enable him to fight alongside the adults in their mission to defend earth. 
Vegeta is a powerful Saiyan. He is a 'Super Elitist' and a prince, the son of King Vegeta, past ruler of the Saiyans. Vegeta and his comrade Nappa are two of the last surviving Saiyans. They come to Earth to destroy all life and sell the planet. Though physically smaller than Goku, Vegeta can power up to unbelievable levels destroying entire planets. He is a fierce rival of Goku's, striving always to seek power levels as high or higher than Goku and to reach Super Saiyan level. Ambitious and determined, Vegeta wants the Dragon Balls to gain immortality. He is determined to destroy Frieza. After th 
Trunks is the son of Bulma, a headstrong technical genius, and Vegeta, one of the most powerful fighters in the Dragon Ball Z universe. His exact age is not certain, but he first appears in Dragon Ball Z in his mid to late teens. He is from the future and has witnessed a threat to Earth which cannot be stopped in that time. He has come back in time to try to save the Earth of his time, only to find our heroes in Earth facing their own peril. Much to the amazement of our friends, Trunks immediately turns Super Saiyan and defeats Frieza and King Cold. He gives Goku medicine to prevent his death from heart disease and tells them of Earth's coming predicament. The Z fighters immediately go into training, and Trunks returns to his own time. Trunks returns to our timeline again in the Android Saga to ensure that the androids do arrive on Earth. He is also born during this saga, so we have the opportunity to see him both as a teenager and a baby at the same time. He continues to exist as a boy and a teen until the end of the Cell Saga, when the older Trunks returns to his original timeline. 
Goten and Trunks form this new entity by the Metamoru art of Fusion, which was taught to Goku and is passed on to Goten and Trunks while Goku is back from the Other World. The fusion must occur between two beings of equal power (Trunks has to lower his power level to fuse with Goten), and is accomplished by a goofy looking, mirror-image dance. This type of fusion only lasts 30 minutes, and they must recuperate for one hour before fusing again. 
Goku's onetime archenemy, Piccolo is the second strongest being on the Earth, born as a concentration of Kami's negative spirits. He has powerful energy blasts, can split into two or four separate entities, and has the ability to regenerate limbs. He is often seen in a white cape. Originally from the far away planet Namek (although Piccolo doesn't know this for a long time), Piccolo starts off fighting Goku to rule the world. When the Saiyans arrive he joins forces with Goku. At first it is an uneasy alliance, but as the story unfolds, their bond becomes stronger. While training Goku's son Gohan for the upcoming battle against the Saiyans, Piccolo develops a special bond with Gohan. Through Gohan, the only person who has ever been a friend to him, Piccolo starts changing character for the better. He ends up sacrificing his own life to save Gohan. While battling with Frieza, Piccolo merges with Nail, the last of the Namekain warriors and former guardian of Guru. From this merging, Piccolo gains Nail's ancient Namek fighting style, greatly enhancing Piccolo's powers and abilities. 
When things become too much for the Z-fighters, Goku and Vegeta must make a difficult decision: perish under Buu's tremendous strength, or wear the fusion earrings, permanently binding them together. When the choice was made, Vegetto was born. Vegettto fights Majin Buu in various forms including Super Saiyan and even as a piece of candy. It is when Vegetto is absorbed into Buu's body that the two warriors separate again. They later decide to remain as individuals. 
The Kaioshin is the highest ruler remaining after Buu's elimination of the other Kais years ago. He becomes the Kaioshin by default, ruling over Grand Kai and thus all life in the universe. He comes to Earth during the World Martial Arts Tournament to warn Goku about Babidi's plan to revive Buu and to prevent it from happening.