system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings] If Gandalf decided to take the Ring for himself and use it, what could he achieve? Just how powerful would he be?
gpt
In his letters Tolkien quite clearly described what someone like Gandalf would do if he were to take the Ring. He'd start building an empire to rival Sauron's and force a confrontation with the forces of Sauron. The Rings main power is in the domination of wills so that'd be the natural application. 

The Ring doesn't instantly transform its wearer into some super-powerful warrior. Sauron himself was beaten conventionally while in possession of the Ring. The confrontation would be very close because Sauron is stronger than Gandalf (he said as much even after returning as the White) but since Sauron has already poured much of his strength in his various failed plots and machinations Gandalf would probably have the upper hand.

In that case Gandalf would then conquer all of Middle-Earth with his legions just as Sauron intended to do. It'd be the end of the free peoples of Middle-Earth but this time by the hands of knights in shining armor instead of orcs.