He can be seen guarding the cage that holds the princess, implying that he is one of the 6 guardians. The other guardians being the Armored Ghost, Armored Fiend, Armored Archfiend, Diamond Golem and Ultimate Ghost. He is made out of iron. He has horns and red eyes. Like all other golems, the Iron Golem will take two less damage from all sword attacks. But unlike most of the golems black magic is ineffective. When he is defeated he turns into purple smoke and the princess is then released from the cage. In the Secret Quest the Iron Golem can be found in the Shrine of Judgment. The amount of HP that he has is 45 HP.
Ironically, the Diamond Golem (found exclusively in the Secret Quest) is vulnerable to black magic, unlike the Iron Golem, even though it is basically a stronger version of the Iron Golem.
The name is also the name of a build able mob from the Mojang game: Minecraft.