The series continues the adventures of Son Goku who, along with his companions, defend the Earth and other fictional planets against various supervillains. While the original Dragon Ball anime followed Goku through childhood into adulthood, Dragon Ball Z parallels his adult life with the maturation of his first child, Son Gohan. The series also gives focus to the evolution of his rivals, Piccolo and Vegeta, from evil to good, with the former's evolution ocurring early in the series and latter's spanning across the entire series. The separation between the series is also significant as the later series takes on a more dramatic and serious tone, with a number of villains either threatening or committing acts of mass murder or outright genocide.