Information: Dragon Ball GT: Saga Summaries
Bebi Saga
Ten years after the end of Dragonball Z, Son Goku gets turned into a child again by a wish Pilaf made. The only way Son Goku can get back in his normal state is by finding the Black Star Dragonballs scattered across space. Son Goku, Pan, and Trunks go on journeys battling minor villans. At one planet, the DragonBall gang stumbles across Bebi. Bebi sneaks on board and lands on Earth. Bebi takes over bodies in hope of finding a good host. Bebi first uses Goten and Gohan as hosts, but he finally finds the most powerful host, it is Vegeta! Vegeta now turns into Bebi-Vegeta. A great battle between Son Goku and Vegeta begins. It turns out Son Goku is no match for Bebi-Vegeta. Then Kaioshin pulls out Son Goku's tail, hoping he can go into Oozaru stage. It works, but Son Goku still cannot defeat Bebi-Vegeta, who now is Super Bebi (Oozaru Bebi-Vegeta). Then something weird happens, Son Goku takes control of his body now and transforms into SSJ4 Son Goku! Son Goku soon defeats Super Bebi. (Note: Bebi-Vegeta can also turn to SSJ4)
Super 17 / Evil Shenlong Saga
In hell, Dr. Gero and Myuu create Artifical 17. Artifical 17 comes from hell to fuse with Android 17, when they fused, they became Super 17. Son Goku gets tricked into going to hell to fight Cell and Frieza, who are already dead. Without Son Goku, the earth is doomed. Piccolo, (who died in the Bebi Saga) and Dende create a portal so Son Goku can get out of hell. Son Goku later kills Super 17. When the DragonBalls are gathered to wish back the people killed in battle something goes wrong. Shenlong says that with all the negative energy the DragonBalls have stored, seven evil dragons have been formed. Each dragon pocess a DragonBall, so Son Goku and the Z fighters go off to fight the evil dragons. When they come up against Li, SSJ4 Son Goku fuses with SSJ4 Vegeta! Making SSJ4 Gogeta. He beats the crap out of him with ease. But Gogeta's fusion span was shortened because of the 4th stage of Super Saiyan. They can only stay fused for 20 min instead of 30 min. Just when Gogeta was about to finish Li, he diffuses. But the 2 warriors eventually killed the worn out Li. When all seven dragons have been defeated, the real Shenlong appears and grants Son Goku one wish, the wish is that everyone killed in battle agansit the dragons to be brought back to life. Shenlong tells Son Goku to get on his back, then the seven dragonball are absorbed into Son Goku, and his whole body vanishes, leaving only his clothes on the ground. Seems that Son Goku is the most powerful fighter in the universe to have the DragonBalls absorbed. Shenlong says he will not grant wishes again for 100 years and then it shows Goku Jr. and Vegeta Jr. fighting. Pan (now over 100, its one of those skip a few years things) sees Son Goku in the crowd then he walks away.