This has been one of the most thought #DragonBallSuper questions before we knew the truth of Goku Black. Was that future tyrant FUTURE GOTEN?! What if that were true? How would that change the story? Would we have a more sad story about #DragonBall having Goku's son being used a vessel by Zamasu in a more twisted manner? So, let's start this off at the point of Zamasu's confrontation with Goku during their own investigations in Universe 10. The kai had just fought a Saiyan, a living being, who had managed to equal him in power...little did he know that Goku had WAY more in the tank if he had called upon it. Can you imagine how he would've felt if he had been completely TROUNCED by the Saiyan? Ooof! Anyway, the kai spent many nights agonising over this good-as defeat of his. He had been wronged quite badly by this interloper and monstrosity of the order that had been in place for countless aeons. In this universe, things start off with the Zero Mortal Plan the way they do in the original, all the way up to the moment with the wish to steal Goku's body...that changes.