IS-1: First production model. Built to combat the German Panther and Tiger tanks. Armed with an 85mm gun and more than 90mm of armor.
IS-2: Looks very similar to the IS-1 but has a modifyed turret to mount a bigger 122mm gun.
IS-3: the IS-3 had a better armor layout than the IS-2 and a diffrent turret (looks like a over turned soup bowl like a lot of post world war two tanks)
The IS-4 was suppose to be the succeder of the IS-3 but was short lived. It had a longer chassis and a diffrent turret.
IS-6: Basiclt a IS-2 but with an electric transmition system.
IS-7: A super heavy tank weighing around 68 metric tones and armed with a 130mm fun with a monster amount of armor. Not taken
IS-10: Aslo called the IS-8/9 but was called the T-10 after the death of stalin. The diffrence between this tank and the IS-3 is a bigger turret, longer chassis, and a better 122mm gun.