Originally Posted by
Laurcus
Breakdown of the sagas and how the enemies were defeated.
Saiyan saga. First villain is Raditz. Defeated by Goku and Piccolo. Killed by Piccolo's Special Beam Cannon. The next two villains are Nappa and Vegeta. Nappa is beaten by Goku using the Kaio-Ken. Nappa is killed by Vegeta for being weak. Vegeta is beaten by Goku, Krillin, and Gohan, using the Spirit Bomb. This Spirit Bomb was made with the energy of the entire Earth, but was small because Goku lost the majority of the energy when Vegeta in his Great Ape form hit him with an energy blast. The bomb was made by Goku, thrown by Krillin, and then bounced into Vegeta by Gohan.
Namek saga. No major villain is defeated in this saga, unless you count Zarbon and Dodoria. This is where Frieza is introduced.
Ginyu saga. The main villain is Captain Ginyu. He's defeated by Goku, Gohan, Krillin, and Vegeta working together. Ginyu is not killed, but is instead put into the body of a toad when Goku turns his body switching technique against him.
Frieza saga. Frieza is the main villain. Goku uses the Spirit Bomb against Frieza. It was made with the energy of the entire solar system. The Spirit Bomb fails to kill Frieza. Goku turns into a Super Saiyan and defeats Frieza in combat. Frieza survives.
Garlic Junior saga. The main villain is Garlic Junior. He's defeated by Gohan when he is trapped in the Dead Zone.
Trunks saga. Frieza and King Cold are the main villains. Both are killed by Super Saiyan Trunks.
Android saga. The main villains are Androids 16-20. Android 19 is killed by Super Saiyan Vegeta's Big Bang. Android 20 is killed by Android 17. Androids 16, 17, and 18 are not killed.
Cell saga. Cell is the main villain. He is not defeated in this saga. Androids 17 and 18 are absorbed by Cell.
Cell games saga. Cell is killed by Gohan with help from Goku using the Father-Son Kamehameha Wave.
Great Saiyaman and World Tournament sagas have virtually no fighting.
Babidi saga. The main villains are Babidi and Dabura. Dabura is killed by Majin Buu when he is introduced at the end of the saga. Babidi survives.
Buu-Fusion sagas. The main villain is Majin Buu. He is not defeated in these sagas.
Kid Buu saga. The main villain is Kid Buu. He is killed by Goku using the Spirit Bomb. This Spirit Bomb is formed with the energy of all of Earth.
It is common among fans to refer to the various sagas by the main villains of the series. Mainly Saiyan saga, Frieza saga, Cell saga, and Buu saga. This is essentially shorthand, as it combines the less important sagas. Many see the 4 main villains of the series as Vegeta, Frieza, Cell, and Majin Buu.