Goku: He is the main character of the Dragonball series. He is a Saiyan who was sent to Earth as a child. The series "Dragonball" is the story of his youth, so I won't go into that. He has two sons throughout the series. They are Gohan and Goten. Gohan is the older son and is present for almost all of the episodes. Goku is one of the most powerful warriors in the universe and is continually training to get stronger. However, he dies twice in the series. The first time he comes back to life through a wish with the Dragonballs. The second time, he is brought back through a sacrifice to him. Goku is also the first Saiyan to turn Super Saiyan.
Gohan: Gohan is Goku's oldest son. He is powerful as a child and continues to get more so throughout the series. He is trained by Piccolo and sees him like a second father. He is very young throughout the Vegeta and Frieza sagas, but as a teenager in the Cell Saga, he is probably the most powerful person in the universe. He eventually earns the title of the "Great Saiyan Man." He is the first to turn into the Super Saiyan form 2. He marries Videl, who is the daughter of Mr. Satan. They have a daughter named Pan, who is a character in Dragonball GT. Unlike Goten, Chi Chi makes him study a lot and she doesn't like his fighting.
Goten: Goten is the son of Goku and Chi Chi . I think Goten was born somewhere near the Buu Saga , he only saw his father, Goku in the Buu saga . The reason Goten barely ever saw Goku is because Goku died the second time before Goten was ever born. Goten is the best friend of Chibi Trunks and is able to do fusion with him to create Gotenks. With Gotenks, he and Trunks can be SSJ3 as Gotenks. Gohan trains Goten, he was suprised that Goten became Super Saiyan at a very young age.
Krillin: Krillin is a full blooded human from Earth. He is one of the weakest of the fighters, but that does not stop him from getting into battles. But he chooses the fights he gets into carefully, and if he can't win, he tries to avoid the conflict at all costs. He is one of Goku and Gohan's best friends and accompanies Gohan to Namek where he is eventually killed by Frieza, causing Goku to turn Super Saiyan.
Piccolo: Piccolo is from the planet Namek. His origins are somewhat mysterious. He was the son of another Piccolo, which was evil. The evil Piccolo came about as a result of a Namek that tried to purify himself by splitting his good and evil side. The good Piccolo mentored Gohan when Goku was killed the first time. He was originally an enemy of Goku, but became his ally.
Vegeta: He is the prince of the Saiyans and one dude that you do not want to mess with. He is ruthless and unforgiving. He has an ego the size of Alaska and believes that he is the greatest warrior to ever live. He eventually becomes a good guy, though not until later in the series. He aids the Z Warriors occasionally, only to ensure that Goku stays alive long enough so he can kill him.
Trunks: Trunks is the son of Vegeta and Bulma. There are actually two of him in the series. The first is Future Trunks who is sent back in time by Bulma to keep Goku from dying. He does this and destroys Frieza and helps in the Cell fight. He eventually returns to his original time strong enough to destroy the androids ruling there. The second Trunks is the young Trunks seen in the last part of the series. He is Goten's best friend. He is trained by Vegeta, who becomes envious of him because he is so strong.
Android 16: He is the other good android. He was Gohan's best friend and it was his death that caused Gohan to turn Super Saiyan form 2.
Android 18: She is one of the good andriods. During the series, we find out that Krillin has fallen in love with her. Eventually, she is wished human and she and Krillin get married and have a daughter.
Frieza: He is the evil of evils. He wants the Dragonballs for immortality to rule the universe. He kills anyone that challenges him, even by asking questions. Extremely powerful, he is also ruthless and does not care who he has to dispose of to get the Dragonballs. He eventually fights Goku, who destroys him by becoming Super Saiyan. He is put back together by his father, King Cold, and is again killed, this time versus Trunks.
Cell: An android created by Dr. Gero. He is incredibly strong and is able to go through a series of transformations. One is where he splits into four Cell Juniors. He also has stages up to his Perfect Cell stage. Once thought to have been defeated, he regenerated from a single cell. When in his perfect stage, the only person capable of defeating him was Gohan in his Super Saiyan 2 form.
Majin Buu: Once released, he is probably the most powerful being alive (without any transformations). He can consume people to gain their powers and does this to most of the characters. However, he is no match for Vegetto. But Vegetto allows himself to be consumed to rescue the others inside of Buu. He is eventually defeated when everyone on Earth raises their hands to give Goku the energy needed to do a seriously massive Spirit Bomb.
Yuzukaa: Goku's ancient old driving instructor who some how survives trying to teach Goku how to drive. After seeing Goku and Piccolo rescue a bus full of school kids, he tells them that guys like them don't need to know how to drive.
Rou Kaioushin: The elder Kai that was sealed in the Z Sword 15 generations before the Supreme Kai, making him very, very old. He is released form the Z Sword when Goku throws the hardest metal in the universe to Gohan who tries and cuts through it with the Z Sword causing the sword to shatter and become the "Z Dagger" as Gohan states in the American Version. This old Kai has the ability to awake hidden powers which he did on Gohan causing him to become a Mystic Saiyan.
Supreme Kai: Supposedly the last of the race of Supreme Kais; he shows up at the World Tournament where Goku comes back for a day after 7 years. Piccolo is the first to face him but forfeits because of some strange feeling he keeps getting about him. Shin Kaioshin turns out to be a weakling when he and Gohan first meet Majin Buu (not to mention not being able to lift the Z Sword). He was the only survivor of the original Buu's assault on the Kais. It turns out Buu ate a really fat Kai and became who we know as Fat Majin Buu. Supreme Kai ends up fusing with his assistant Kabito becoming Kabito-Kai.
Kabito: This is the loyal assistant of Supreme Kai. You first see him when he and Shin show up at the World Tournament. He was killed by Dabura but brought back to life by the Dragonballs. He found the beaten and staggering Supreme Kai and healed him using his healing abilities. They then find Gohan and take him to the Kai planet which Kabito greatly objects to because no mortal has ever set foot on the Kai's planet. Kabito ends up fusing with Supreme Kai to become Kabito-Kai.
Kabito-Kai: Kabito Kai is the fusion of Supreme Kai and his assistant Kabito. This hybrid form has long hair like Kabito's and wears a cross between Supreme Kai's and Kabito's cloths. He fused by the way of the Kai earings and did not realize he would be stuck like that forever until after they fused. This new Kai turns out to be a much stronger guy but is still no match to stand a chance against Buu.
Pui Pui: He is the fighter at the first floor of Badidi's ship. He is from the planet Zun that has gravity ten times that of Earth's. Badidi makes the first floor like Zun using his magic to give Pui Pui the advantage. However, that doesn't help much in winning see as Vegeta has gone over 400g's of training. Pui Pui is destoryed with ease.
Porunga: This is the Namekian version of Shenron. He is a much larger dragon than Shenron is. When you first see him he has better features than the Earth's dragon, for example, three wishes at one time.
Shenron: Created in the year 470, he is the dragon god who comes out when all of the seven dragonballs are brought together and someone says, "Come out Shenron!". He is the one that grants all the wishes for Earth.
General Tao: He is known throughout the world as a lethal assassin. He is hired by Red Ribbon to take out Goku. Goku had gone up the Corin Tower to get stronger, which he did, and defeated Tao with Tao's own gernade. Tao comes back as a Cyborg in the twenty-third World Tournament to defeat Tien for betraying his brother. Cyborg Tao is the one who gavve Tien the scar on his chest. Tao is finally destroyed by Gohan in the peaceful days before the Cell Games.
Yajirobe: He is a fat little short guy that carries a sword. He is a monk. He meets Goku for the first time during the Piccolo Diamaou saga of Dragonball. He shows up a lot in the DB/Z series but kind of loses his neediness near the end of the Z series.
Tenkaichi Budoukai Announcer: The blonde haired announcer for all of the World Tournaments in every DB series. Everytime the ZFighters gang fought he would cover for the subhuman feats that the gang does so the crowd wouldn't be totally bewildered.