This saga takes place seven years after the defeat of Omega Shenron. In this version of events, Goku had been restored to adulthood and stayed to live life with his family. However, the newfound peace would not last. During this time! a new evil emerged.
The evil was in the form of Goku's deceased older brother Raditz, but it was not the Raditz that had died at the hands of Piccolo. For you see, Raditz's evil side had completely separated from his good half and started rampaging in Hell. This purely evil Raditz's body is fully blood red with his power reaching beyond what Raditz had ever achieved.
Despite this, evil Raditz was defeated by Super Saiyan 5 Goku. Before being sent back to Hell, the evil Raditz warned Goku that it had been King Vegeta's evil half that had been behind it. He also told him that his good half, along with Nappa's and King Vegeta's good halves had gone to King Kai's planet. Finally, he reveals that in order to TRULY defeat the evil sides, he had to obliterate them with their good sides.