It’s probably this guy:

Vice admiral Vasily Arkhipov.
During the Cuban Missile Crisis, Arkhipov commanded a flotilla of Soviet submarines. On October 27, 1962, he was aboard the B-59, cruising deep underwater in the Caribbean, when the sub was discovered by U.S. Navy ships. The Americans started firing depth charges, meant simply as warning shots, but the B-59 crew had no way of knowing this. The sub was too deep underwater to pick up radio signals, and these were fraught days. No, the B-59’ers worried war had broken out.
Assuming his ship was under attack, Captain Savitsky readied a nuclear torpedo. But launching nuclear weapons required the authorization of three senior officers on board. Only Arkhipov held out. Apparently, the dispute got pretty heated. Despite what must have been some wildly intense peer pressure, Arkhipov refused to sign off on the launch. Had he buckled, the world almost certainly would have tipped into a Dr. Strangelove-type doomsday scenario.
Here’s a picture of the submarine that almost started a nuclear war.

There are a strangely high number of stories about how close we’ve come to nuclear war only to be saved by some tiny quirk of fate. Wikipedia has a whole list of close calls. This Business Insider article does too. The fascinating Cold War book The Spy and the Traitor details another near-doomsday caused mainly by panic and paranoia. In many cases, the fate of the world seems to hinge on one person not being nuts. Really, it’s a miracle we haven’t killed ourselves a thousand times over. It’s practically an argument for the existence of God.
Of all those shaky for-God arguments, the fact that we have repeatedly been saved from a species-wide self-destruction seems to me as compelling as any other. Despite our best efforts to do ourselves in, mysterious–almost fluky–forces keep pulling us back from the brink. So far, at least … but stay tuned.