Goku is one the strongest fighters in the universe.
First coming to the planet Earth as a space pirate Goku was meant to rid the planet of the human race. He failed to carry out his mission because of a mind-rupturing accident in which he fell into a deep ravine. From then on he had remebered nothing about his past and became a worrior under the training of Master Roshi.
He also has the ability to become more powerful after every fight as saiyans do and is the first to reach a level that was thought only to be a myth....Super Saiyan. He has a wife name Chi-Chi and two sons, one he names after his adoptive grandfather Gohan, and another named Goten. Goku is a good-natured person and loves to fight like all saiyans do. He seems to be too trusting at times but always willing to take that risk.

Gohan is an extremely powerful fighter who was born under Chi-Chi and Goku.
His mix of Saiyan and Human is where Gohan gets alot of his raw power from. Goku doesn't see this power until he and Piccolo fight Raditz and he becomes so upset that he ends up hurting Raditz. Piccolo also sees this so he kidnapps Gohan to train him and teach him how to use his power. He grows up fast and his power also increases after every battle like his father's.
Chi-Chi is very protective of him and pushes him to study rather than fight. Even though he has great power he never loved to fight like his father has.

GOHAN

GOKU

KRILLIN

Krillin is one of the Earth's strongest fighters.
He's small and doesn't look too dangerous but don't be fooled, he can hold his own agianst other strong warriors.
Krillin is Goku's best friend and buddy ever since they were little and trained under Master Roshi. He also brings comedy to the scene and always keeps the Z warriors laughing. He holds friendship as a very high priority and always seems to keep his hopes high.
After awhile he settles down and marries android #18 and they have a daughter named Marron.

VEGETA

Vegeta is the prince of the saiyans on the planet Vegeta. Brought up in an environment full of violence Vegeta has grown to be a ruthless killer and relentless person. When he was little his father was killed by Frieza and was one of the four to survive Frieza's destruction of his home planet.
He first comes to earth as to see why Raditz has not return and finds out that he was defeated by Goku known as "Kakarot". He battles Goku only to learn he isn't strong enough to defeat him. After dying on Namek he reflects on his life and starts to become a "good guy". He joins the Z warriors but only to ensure that Goku stays alive so he can kill him.
He also settles down and marries Bulma and they have a son named Trunks

PICCOLO

Piccolo is another among the strongest fighters on Earth. Piccolo is the evil half of an older piccolo with Kame being the other half.
At one time he was Goku's enemy but, Piccolo decides to team up to fight against Raditz and he later develops a friendship with Goku.
Piccolo also trains Gohan to use his powers and from then on they develop a special bond which causes him to sacrifice himself for Gohan. While training Gohan he starts to feel things that he had never felt before.
During his stay on Namek he merges with Nail and later merges with Kame to become one of the strongest Namekans ever. A Super-Namek. He is also always focused on improving himself to become stronger.

FREEZA

Freeza is one of the most powerful and evil beings in the universe.
When he learns about the Dragon Balls he is crazed with the idea of finding the Dragon Balls and wishing for eternal life.
Knowing about a saiyan's ability to become more powerful after injuries and battles, Freeza feared that one day a saiyan would raise up and contest his power so he decided to wipe out the entire saiyan race by destroying planet Vegeta. Little did he know that that saiyan would be Goku.
Freeza is extremely powerful and strikes fear into those when even his name is mentioned. Even though Freeza is defeated on Namek he is later returns to Earth with his father King Cold to get revenge against Goku and the other Z warriors.

TRUNKS

Trunks is Vegeta's and Bulma's son.
When he first appears he came from the future. In his timeline the Androids kill most of the Z worriors and Goku dies of a heart attack, but he travels back in time to warn Goku of the arrival of the androids and gives him medicine to prevent his heart attack. For some reason Trunks decides to stay in this timeline for a little while. Even at one point Trunks exists in the same timeline with his younger self.
Trunks has a "pure heart" and is a very good and powerful fighter. When Trunks was a child he was best friends with Goten (Goku's second child) and they were inseperatable. They both were very michevious and get into trouble alot

YAMCHA

Yamcha is another one of the earth's most powerful fighters.
His expertise is in energy ball and channeled energy attacks. He isn't as strong as some of the other Z fighters but he can always come in handy.
Yamcha was once a desert bandit where he met Bulma and Goku on their search to find the dragonballs. He has a cat friend named Puar who can tranform in shape and size.
He also is afraid of women but, he gets over this fear and asks Bulma to go on a date. Instead he stood her up and claimed he didn't have enough money.
Yamcha is also a pretty good fighter and is dedicated to training and fighting.