Arrival of Raditz
After the end of Dragonball everyone has settled down and has become older.While they were having fun a misteryious person appered and said his name was Raditz he then went forward and explained Goku's heritage and said he was Goku's brother.Raditz stated that Goku was to kill 100 humans or he would not see Gohan again. Picolo was attacked by Raditz earlier and decided to become good and help Goku fight Raditz. Goku and Picolo appered and they started the battle but were no match for the Saiya-Jin. As Goku was screaming in pain at the hands of Raditz Gohan heard the screaming and got angrey he then attacked Raditz with such force that he broke Raditz armor. Picolo and Goku then made a plan. Goku then grabbed Raditz and Picolo did a maximum Makakenapusoo(Demon Ray/ Special Beam Cannon) which killed Raditz and Goku. Goku asked Picolo to wish him back with the dragonballs.
Vegeta and Nappa
In raditz last word he stated that a pair of incrediablly stronger Saiya-Jin would come to avenge his death. So the Z-warriors formed and started there training so did Goku upon King Kai's tower. Goku was wished back as the Z-warriors were fighting the Saiya-Jin duo.But Goku was to late to save Picolo and Tien and Yamcha, by the time he arrived Picolo just got killed by Nappa saving Gohan.Gohan and Krillian were save so Goku started the battle. Goku easily beat Nappa who had beat Picolo, Tien, Choutzu, and Yamcha together.Goku then fought Vegeta. After a long and equal battle Vegeta turned into the Oozaru monkey and his power was greatly increased. Vegeta was later brought back down to regular and Gohan had also reached Oozaru and helped Goku defeat Vegeta.