There are three sets of Characters on Dragonball Z: The Z Fighters, Enemies, and Other Good Guys
The Z fighters are the defenders of Earth and the Universe. This consists of Goku, who is the head of the Z fighters. Piccolo is the Namekian of the Group. Piccolo is the strongest non-saiyan that is in the Group. There is Gohan who is the first son of Goku. He has a hidden power unmatched by anyone, that is released only when he is angry. Vegeta is the prince of the Saiyans. He always tries to surpass Goku in power but always fails miserably. Trunks is the son of Vegeta. He destroyed Frieza and King Cold. He was trained by Gohan. He is always seen with Goten. There is Goten who is the second son of Goku. Goten is an complete idiot. He looks exactly like Goku. Krillin is the best friend of Goku. Krillin is there basicly for comic relief. He developed the Destructo-Disk technique. Tien is the bodyguard of Chiaotzu. Chiaotzu is an Emperor, he always fights and trains with Tien. Yamcha is one of the few humans that fight in Dragonball Z. These are all the Z fighters.
Other Z Fighters
These are creatures, things and beings that try to destroy the Earth and take over the Universe. Starting from the beginning Raditz came. Radditz is the older brother of Goku. He gets defeated when Piccolo pierces him and Goku with the Special-Beam Cannon. Then Vegeta and Nappa came. Vegeta was the prince of the Saiyan Race. He wanted to become immortal so that he could rule forever. Nappa was brute force with no brain. He was first disabled by the Kaiou-Ken Technique. He is then sent to another dimension by his friend Vegeta. Then they went and they met Frieza who was the most powerful being in the Universe. He was destoryed when he kill Krillin and pushed Goku over the edge. Goku turned Super Saiyan and almost destroyed Frieza but Frieza survived Namek exploding. When they got back and then Garlic Jr. came back. Garlic Jr. was imprisoned in the Dead Zone by Gohan. Frieza came back with his father and they both were destroyed by future Trunks. The Androids were Dr. Gero fighting machines. Android 17 and 18 were absorbed by Cell. Android 18 was thrown back up. Android 16 was destroyed by Cell. Cell was destroyed by Gohan with a little help from Vegeta's Big Bang Attack. Buu???
Other Good Guys
The other good guys are basicly those who don't do really anything important or significant. This is Chi-Chi, Ox King, Dende, Kami, Mr. Popo, Master Roshi, Bulma, Dr. Brief.
Other Good Guys