The T-55 is a Soviet-made main battle tank that was produced from the 1950s to the 1980s. It was the most widely produced tank of the Cold War era, with over 86,000 units manufactured. The T-55 was designed to replace the T-54,
From Wikipedia
The T-54 and T-55 tanks are a series of Soviet medium tanks introduced in the years following the Second World War. The first T-54 prototype was completed at Nizhny Tagil by the end of 1945. From the late 1950s, the T-54 eventually became the main tank for armoured units of the Soviet Army, armies of the Warsaw Pact countries, and many others. T-54s and T-55s have been involved in many of the world's armed conflicts since their introduction in the second half of the 20th century.