The Soviets built 3800 IS-2 tanks. They built IS-3s and IS-4s, but not until after the war. This tank was created to stop German pillboxes, AFVs or any kind and any combat engineered obstruction created for the Red Army. The 122mm gun of the IS-2 could penetrate the glacis plate of a Panzer Mark V Panther . It served to finally give the pursuing Soviets a game changing gun platform. The IS-2 was a match for Panthers and Tiger I tanks. In fact, it was the most heavily armored tank in the world at the time.
Sources: wiki, Tanks, History Channels