Dragon Ball
Long before Dragon Ball Z, there was a series called Dragon Ball. It was a series that chronicled the adventures of one mischeviously natured boy named Son Gokou. The story begins with Bulma, daughter of the super-wealthy owner of Capsule Corporation, accidentally crashing into Gokou. The story mainly revolves around the mysterious past of Gokou, but after meeting Piccolo Daimaou the story really gets complicated. I really felt that was one of the reasons the series faltered in the end which was the fact that the power level system of Saiyans were so unfathomably high. The series changed to Dragon Ball Z after the Tenkai Chi Bodoukai, a fighting tournament, where Gokou defeats Piccolo.
Introduction To Dragonball Z/GT Sunny's Dragonball Village