Sszark the Burning is a Super Unique Flame Spider found in the Spider Cavern, a dungeon below the Spider Forest, in Act III of Diablo II. He is found near the golden chest that contains Khalim's Eye and most often must be killed before obtaining the Khalim's Eye, as he blocks the path to the chest.
Sszark is a deceptively dangerous monster. Giant spiders aren't generally that difficult, and Flame Spiders do not have poison damage, but they have a lot of hit points, they do considerable damage with their bites, and Sszark is Extra Strong and Cursed. Facing him and his pack in a small cave area without room to retreat can be quite dangerous.