The device was created in 1947 by scientists, but it has been adjusted 19 times, because not always worked accurately.
Doomsday clock normally shows how close humanity is to catastrophic destruction. It was closest in 1953 at 2 minutes to midnight. Coincidence or not, but right then the United States tested its first thermonuclear device, distroying a Pacific Ocean island in the procedure and just nine months after the U.S. tests, the Russians (Soviet Union) tested an hydrogen bomb.
According to Bulletin of the Atomic Scientists, the mankind was farthest away from an apocalypse in 1991 – 17 minutes to midnight. At that time the Cold War ended. Scientists must constantly decide when and if the Doomsday clock must be adjusted.
Now the clock is just 5 minutes to midnight and is still ticking.