In its conclusion, a leader 30,000 years in our future views himself in a room with two other versions of himself, and realizes he was the "Diktor" he met as a young man all along. Diktor then sends a younger version of himself back through the Time Gate, thus ensuring his own existence with no outside help (unless, of course, you count a time machine). Name this 1941 Heinlein story.
By His Bootstraps