Dragon Ball Z was adapted from the manga Dragon Ball created by [Akira Toriyama]?. The main character is Goku, an ultra-strong, yet simpleminded and kindly character. After a visit from his previously unknown brother, he discovers that he is an alien that was sent to Earth to destroy it. When he informs his brother Raditz he no intention of doing this, Goku and his friends become the erstwhile defenders of the Earth from the oncoming invasion by more of his kind.
As the series progresses, Goku, his son and their companions age, get immensely stronger, and fight increasingly powerful and sinister villains. Many of the main characters die, are resurrected, get married and/or have children. The series has had a dramatic progression throughout its entire run.
Many important facts were introduced into the series that add a different story arc to Dragon Ball Z from its predecessor:
Goku is an alien from the planet Vegita. This is the source of his previously unexplained abilities, and why he has a tail.
Goku's enemy from the first series, Piccolo is an alien from the planet Namek. He is the product of Kami (guardian of Earth) splitting himself in half to purge the evil from himself.
The origin of the dragon balls as the product of Kami.
The series can be logically broken into sagas based on the current enemy:
The Frieza saga
The Cell saga
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