This is one of the more imaginative stories of Clarke. And well told.
And this story could not have been possible if quartz watches were around when the story was written. That should tell something of the age of the story.
Story summary (spoiler).
First thread of the story, the one involving the war monger ("Master"), begins almost in our time. After bringing a lot of world to ruin, Master is facing definite defeat soon. He is currently hiding somewhere in the Himalayas with with his coterie.
That is when he takes extreme action. Kills his coteries by deceit by assembling them in a gas chamber, & activating it after own escape.
He has already prepared a hibernation chamber for self in a cavity deep inside a Himalayan mountain. Inaccessible with the only entries sealed under massive piles of rock. Explosives are planted to blast himself out after awakening.
Goes to hibernation for 100 years. Any earlier appearance will mean definite trial for war crimes; any later, & world would have changed so much that he won't really be able to dominate.
Only problem is: all the fancy hibernation gadgets depend on a rather rudimentary clock. It is a kind of light sensor outside the mountains. It counts days by watching the sun's rise & fall. While it is triplicated, all three sensors are destroyed by a falling bomb while the war is still in closing stages.
So the dictator sleeps not for 100 years, but through geological ages. His mountains have been under the seas, risen again, & now slowly eroding with winds, rains, & snow.
Second thread of the story begins at this stage. Humans have been occupying the far flung reaches of galaxy for untold eons. And we see a trial of a philosopher for hearsay. The trial is very similar in spirit to Plato's "Apology" (though Apology is a far more readable book).
Philosopher refuses to change his opinions. Three options are presented: kill him (unthinkable - capital punishment has been off bound for eons); modify his mind using a machine (unthinkable - he is one of about a dozen best brains galaxy wide); & send him via a time machine to a future where his opinions can no longer affect human affairs.
Third option is adopted. He is sent, with ample supplies (including a building & a flyer), to earth at a time when earth has become a dead planet. Sun is much colder, earth is mostly a desert, & a day on earth is much longer.
He explores the earth after arrival in new time - a small place in his flyer, almost the sole living being on the planet, though air is still breathable.
That is how he encounters the hibernating Master, & awakens him. Now the philosopher comes from a era where telepathy was common. As Master is awakening, the philosopher learns of his deeds & targedy by probing his mind.
And kills this bad sample of humanity, choosing to live alone on this desolate earth.
- Robert Heinlein's "Successful Operation": Another story where a dictator meets an unwelcome end.
Exile of the Eons, short story, review
Author: Arthur C Clarke
This story has also been published under the following titles.