What is Dragon Ball Z?

Dragon Ball Z is a manga and an anime about an alien man who comes to Earth named Goku. It picks up the show from its prequel Dragon Ball and is analogous to Superman. Goku  is a Saiyan, a race of fighting aliens, and as an adult, he and his friends, the Z fighters, defend the Earth from other Saiyans such as Raditz and Vegeta, alien overlords such as Frieza, androids such as Cell, and magical creatures such as Majin Buu.