Dragon Ball Z (ドラゴンボールＺ, Doragon Bōru Zetto; commonly abbreviated as DBZ) is the long-running sequel to the anime Dragon Ball. The series is a close adaptation of the second (and far longer) portion of the Dragon Ball manga written and drawn by Akira Toriyama. In the United States, the manga's second portion is also titled Dragon Ball Z to prevent confusion for younger readers.
Dragon Ball Z follows the adventures of the adult Goku who, along with his companions, defends the earth against an assortment of villains ranging from intergalactic space fighters and conquerors, unnaturally powerful androids and near indestructible magical creatures. While the original Dragon Ball anime followed Goku through childhood into adulthood, Dragon Ball Z is a continuation of his adulthood life, but at the same time parallels the maturation of his son, Gohan, as well as characters from Dragon Ball and more. The separation between the series is also significant as the latter series takes on a more dramatic and serious tone. The anime also features characters, situations and back-stories not present in the original manga.
Filler is used to pad out the series for many reasons; in the case of Dragon Ball Z, more often than not, it was because the anime was running alongside the manga, and there was no way for the anime to run ahead of the manga (since Toriyama was still writing it, at the same time).
The impact of Dragon Ball Z is enormous. For more than 20 years, the series has stood the test of time and has reached out to many children and adults alike across the globe. This is mainly due to the series' very clear representations of good overpowering evil, love overpowering hate, the importance of family and friends, and an unyielding passion toward achieving goals. The series also featured heavy sci-fi overtones, and a greater emphasis on fighting - making it extremely popular among adolescent boys who had grown up alongside the original series.