The Variable Man
What or Who is the Variable Man?
"The Variable Man" is a short story by Philip K. Dick that can be found in his collection of short stories named "Beyond Lies The Wub".
Spoilers
In the story, the Terran system (our system) is growing all the time, but an old and corrupt Centurian Empire is holding Terra down because it encircles the Terran system and wont let the humans grow out of their current empire. For this reason Terra is at war with Proxima Centuri and is trying to find a way of "Breaking Out" from the Centurian noose around its neck.
In the war, Terra is continually coming up with new weapons to try and break centurian defenses, but Proxima Centuri is also continually updating its defense. Using spies and other such tactics both parties find out about each others advancement, and no actual fighting ever happens because both sides are too busy trying to beat each other with the technological developments. Until one day Terra comes up with a concept for a bomb, a bomb that Proxima can not defend against. Then the "odds" start to side with Terra and Terra starts preparing to fight with it. The only problem is that the bomb doesn't work yet.
This is where the variable man comes in. The Variable Man is a man from the past. He is brought into the current (or future depending on perspective) via a Time Bubble as an accident. He escapes from the authority in the future and spends a lot of time running from them afterwards. It is, however, discovered that this man has a certain genius to fix things and make things work. This is because he comes out of a period when humans had this natural genius and knack to invent things and solve problems. It is at this point that the man working on the FTL (Faster than Light) bomb realizes that The Variable Man is the only person who can make his bomb work. And thus, he gets him to help out.
The bomb eventually works, though not in the way that anyone would have guessed. I will leave to rest to you to find out...
Go read the story.