Short answers, pulled from the story.
The RSD-10 Pioneer was an intermediate-range ballistic missile that carried a nuclear warhead, deployed by the Soviet Union from 1976 to 1988 to strike targets across a wide arc from its launch sites. NATO reported it under the name SS-20 Saber.
NATO reported the RSD-10 Pioneer as the SS-20 Saber. An upgraded variant, the Pioneer-UTTKh, later received its own NATO reporting name, SS-28 Saber 2.
Deployment of the RSD-10 Pioneer commenced on the 11th of March 1976, with the first units becoming operational that August. By 1986, 435 RSD-10 missiles were in place across 48 launch sites.
The RSD-10 Pioneer gave the Soviet Union an in-theater targeting capability that could destroy NATO bases and installations with negligible warning. In 1979, NATO responded by deciding to deploy Pershing II missiles and BGM-109G Ground Launched Cruise Missiles in Western Europe, a move known as the Double-Track Decision.
A total of 654 RSD-10 missiles were built. Under the 1987 Intermediate-Range Nuclear Forces Treaty, these missiles and 499 associated mobile launchers were destroyed by May 1991, with fifteen RSD-10 missiles preserved to commemorate the agreement.
A preserved RSD-10 missile stands at the National Museum of the History of Ukraine in the Second World War, another is at the Ukraine Air Force Museum in Vinnytsia, Ukraine, and a third is inside the Smithsonian National Air and Space Museum in Washington, D.C.