Most pivotal citizens in US history.

[Spartan Squad]

Where does Oprah fit?

 

[Huggy]

Young Cashius Clay started boxing because someone stole his bike. I'm not sure even he saw where his life and career as Muhammad Ali would take him.

 

[DanOregon]

Willis Carrier

If air conditioning were never invented, we would have never met "Florida Man" - Arizona would still be a desert and the electoral college would look much different.

Side note - I included a "no gun" qualifier - but with guns, you'd have to go with Booth right? Johnson made a shambles out of Reconstruction after Lincoln died. Maybe Abe wouldn't have been much of a hard-liner and Congress would have had his back - but it would have been a lot different.

 

[Neutral Corner]

Thomas Alva Edison.

 

[Liut]

Frank Wills, the Watergate security guard who discovered the break-in. The details may have come out eventually, but he got the ball rolling.

Or the dumbash who taped the lock over the second time.
IIRC, it was James McCord but not sure, obviously. Maybe he actually was still working at CIA.