1957
Launch of Sputnik I and II - the Soviet Union takes the initiative in the Space Race by launching two satelites into orbit, the second containing Laika, a stray dog

A technician tinkers with Sputnik I

The rocket that carried Sputnik I, on the launch pad

Stray dog Laika would make it into the history books, becoming the first dog in space on 31 October 1957. However, she would not survive, and after 2,570 orbits, Sputnik II — including Laika's remains —disintegrated during re-entry on 14 April 1958.

A technician tinkers with Sputnik I
History was made on October 4, 1957, when the Soviet Union successfully launched Sputnik I. The world's first artificial satellite was about the size of a basketball and weighed only 183 pounds. It took about 98 minutes for Sputnik I to orbit the Earth on its elliptical path. The launch ushered in new political, military, technological, and scientific developments and marked the beginning of the space race between the U.S.and the U.S.S.R.
The Sputnik launch changed everything. As a technical achievement, it caught the world's attention and the Americans off guard. The public reacted with fear that the Soviets' ability to launch such a satellite would translate to the ability to launch ballistic missiles that could carry nuclear weapons from Europe to the U.S.
Then the Soviets struck again: Sputnik II was launched on November 3, carrying a much heavier payload and a dog named Laika (who made it into space but never returned to earth).
The U.S. Defense Department responded to the political and public furor over the Sputnik satellites by approving funding for a U.S. satellite project (which would launch the Explorer satellite on 31 January 1958).The Sputnik launch also led to the creation of NASA, the National Aeronautics and Space Administration in July 1958.
SOURCE: ThoughtCo.com
Further Reading
Cosmos Magazine - How Sputnik 1 Launched the Space Age
SF Gate - Sputnik: The Little Metal Ball that Fueled the Cold War