Mike Resnick recommends 4 novels by Olaf Stapledon

In this tribute titled "The Greatest Thinker of Them All".

Begin with:

1. "Star Maker": "which is nothing less than the history of this and every other universe ever to exist from the beginning to the end of Time. Brian Aldiss has argued that this is the most important science fiction book ever written; I have shared that opinion from the day I finished the book more than 40 years ago."
2. "Last and First Men": "follows the human race through eighteen startling evolutions for more than two million years, until our eventual extinction".

Later:

1. "Odd John": "first novel of a mental (rather than a physical) superman".
2. "Sirius": First story "about a dog with artificially enhanced intelligence".

There is a warning too: read him for innovation rather than literary quality.

I haven't read any of these books.