The transformation in the character of Gully Foyle is truly astounding. He starts this novel as a nobody, a selfish Mechanic's Mate 3rd class without education or any trappings of sophistication. He ends up becoming the next stage in the evolutionary development of the human race, learning some massively important lessons on the way and being able to usher on his species into the same position that he holds. Gully Foyle starts off as a character consumed with revenge, determined to find the ship that could have saved him when he was shipwrecked on the Nomad, but didn't. On his quest for revenge, he is forced to adapt and develop supernatural powers that separate him from the rest of his species. However, by the end of the novel, what replaces revenge is social awareness and responsibility that demonstrates the moral transformation he has undergone. This is shown most clearly when he gives all of humanity the same powers to destroy the world that he has learned from discovering the secret of PyrE. Note what he says as he gives this power:

Take a war to make you spend. Take a jam to make you think. Take a challenge to make you great. Rest of the time you sit around lazy, you. Pigs, you! All right, God damn you! I challenge you, me. Die or live and be great. Blow yourselves to Christ gone or come and find me, Gully Foyle, and I make you men. I make you great. I give you the stars.

Foyle's reasoning is that if all of humanity has the same power to destroy the world, then there will be an incentive for nobody to do so, and that this power will force the rest of humanity to evolve in the same way that he has to be able to cope with this power and use it wisely. Sharing the secret of PyrE with everybody means that there will be some sort of Mutually Assured Destruction that will jolt humans into a new understanding of social consciousness. Gully Foyle therefore changes dramatically during the course of the book.