Vegito and Gogeta are currently the strongest mortals ... However, it was only really brought to the forefront of the series in the Majin Buu Saga, where Goku and Vegeta would unite their ...

The first ever fusion of Goku and Vegeta into Gogeta (in the non-canon film Fusion ... s development was in the final battle against Kid Buu, he openly admits that Goku is the strongest fighter.