I'm not sure if Star Kings is the title, or just what I remember. The book is about two men, one of which is named Caesar Smith, who are on a spaceship away from Earth when Earth destroyed. They are chased but evade, and over a huge amount of time become the power of the universe, modifying them to remain living and increase their strength and abilities. I've been looking for this book for about a week now, and have not found anything on it. I'm sure someone out here can at least tell me the exact title, if not the author. The copy I read back in the sixties was part of a two in one novel (the ones where you can flip them there's another book) and I'm pretty sure the other book was called Prism.