Goku- is the main character in all of the Dragonball series. In Dragonball he was a young boy who went on a search for the Dragonballs with his friends. In Dragonball Z he is older and grown up. He is the most powerful character in Dragonball, and most of the time he is the one to defeat evil like Freeza, Vegeta and so on. He is also the first one to go Super-Saiyen. Goku is very light hearted and may be a little too trustful. He is never afraid to fight, and fights for his friends and the entire universe.
Gohan- is Gokuís son. He first appears in Dragonball Z at the age of 4 I think. He is very powerful, much more powerful then Goku was at his age. He reaches Super-Saiyen in the Room of spirit and time training. He is the first one to reach super-saiyen level 2. As the show moves on he grows up and in GT he is some what of a super hero, named the Great Saiya Man. At the end of the series I think hes in his 20ís. Gohan doesnít like to fight, he tries not to get in fights but if he is forced into it he will give it all he has.
Goten- is Gokuís second son. He loves to fight and reaches super-saiyen at a very early age, even earlier then Gohan. His best friend is present Trunks. Trunks and Goten seem to get in alot of trouble. Also if Goten and Trunks fuse they become Gotenks.
Vegeta- is a full blooded saiyen. He was one of Gokuís first opponents in Dragonball Z. Vegeta used to be evil but after the Freeza saga he seemed to turn toward the good side. Vegeta is very strong and reaches super-saiyen a little after the androids arive. Vegeta is very quiet and stuburn. Vegeta is married to Bulma. He is bent on being stronger then Goku but never is able to reach that goal.
Future Trunks- is Vegetaís and Bulmaís son. He is very calm and nothing like Present Trunks. He is very strong but seems to keep his emotions in check. He is so calm because in his time Vegeta was dead when he was only a small boy. So he never had the influence of Vegeta. He comes to the present in the Cell saga, helps the Z team fight and trains with them. In two words, bad-ass.
Present Trunks- Very rowdy child. Ritalin just never worked for him. It's a shame really. He had the influence of Vegeta and that is why he is so different from Future Trunks. His best friend is Goten, and they get in all sorts of trouble. He is one year older then Goten and he also reaches super-saiyen at a very early age.
Piccolo- was born from Kami, yeah ill explain. When Kami became guardian of earth he had to get rid of all his evil. All of that evil was combined into Piccolo-Damioh. Damioh was an enemy of Goku. When Goku killed Piccolo-Damioh he spit out an egg. That egg hatched and out came the Piccolo we all know and love. He was almost the same and still hated Goku. During the Vegeta saga Piccolo becomes good and joins the forces of earth to fight all evil. Piccolo is a very quiet person. He is strong but can not always keep up with the power the Saiyens have.
Krillin- is Gokuís best friend. He is a earthling and has no nose. When he first meets Goku they both train under Master Roshi. Krillin fights in most of the battles Goku fights in. Krillin can not keep up with the growth in power like the Saiyenís. He is not much help most of the time. I mean, one kick to the freakin' head and he's out cold? Come on.
Freeza- an evil emperor bent on ruling all of the know universe. He is the son of King Cold. We first meet Freeza in the Freeza saga :). Freeza is very powerful at the time. He almost kills all the people on Namek, but then Goku interveens. Freeza was winning the fight but then Goku turned super-saiyen and took Freeza down. Freeza comes to earth for revenge but is killed once and for all by Future Trunks.
Cell- is made up of genes of many great fighters like Goku, Vegeta, Piccolo, and Tein. Cell was created to be the ultimate fighting machine, Dr. Gero, Cellís creator, gave up on Cell but the computer continued to work on Cell untill he was complete. The computer tell Cell that to become perfect he must obsorb #17 and #18. So Cell goes back in time. (in cells time #17 and #18 are dead) Cell can not fit in the time machine so he goes into egg form and is warped to earth. On earth Cell grows and hatches. He then searches for #17 and #18 and absorbs them. Gohan destroys Cell when Gohan goes super-saiyen 2.