In the fictional universe of Warhammer 40,000, the Iron Warriors are one of the legions of Chaos Space Marines. The Iron Warriors' speciality lies in siege warfare. As a result they dislike close combat and instead prefer to sit back and blast their enemies with huge fire-power. Like their primarch, they excel in siege-warfare tactics.

Their colour scheme of preference is silver (Boltgun Metal) gold (Shining Gold) and black (Chaos Black). Their weapons are usually embossed with yellow and black stripes, such as would be used to represent danger or warning. They make extensive use of tanks and heavy artillery, preferring to drop back away from an assault even at the risk of losing a strategic point of advantage and try to eliminate the attackers as they are being chased. They prefer not to go in for an all out assault (such behaviour would be expected of an army of Khorne, for example.).

The Iron Warriors were originally one of the most respected Legions of the Adeptus Astartes, but their Primarch Perturabo led them into Chaos. Perturabo believed that the Emperor used them to fight the Imperium's bloodiest battles and divert the glory and fame to the more favored Primarchs (such as the Ultramarines, Imperial Fists, Space Wolves, Blood Angels and Dark Angels). Every battlefield they dominate on they erect a stronghold that is virtually impregnable by enemy forces, and can be held by as few as six Iron Warriors. Similar to the favoured numbers in God-devoted Chaos Legions, the Iron Warriors are rumored to favor squad sizes in multiples of three.