Iron is Halo 3's second skull and the second skull on the first level, Sierra 117. It is the game's first gold skull.

As a gold skull, it gives you and your cooperative play teammates the Iron achievement if any player picks it up during the game. After picking it up, it can be activated in the campaign settings page of the pre-game lobby.

When activated, this skull will force all cooperative players to reload the previous checkpoint if any of the players die, and will force a solo player to repeat the entire level if he or she dies.

In return for this, it triples your score in campaign scoring.