Iron Warriors

Iron Warriors are a bunch of Badass pricks who are robotic and torture,maim and burn down their old shit. A Chaos Legion specializing in breaking sieges (as in, taking a fortified location, though logically this should mean that they can do this and break out of a siege) which is shown in their love of artillery and greater focus on ranged combat, which stands in contrast to the other chaos space marine legions who are far more disposed to melee combat. They take no shit, but nobody at GW can decide on how they want to portray the Legion. Like we care what they think anyway! They also have a lot of Obliterators which are a bunch of muscle blobs armed to the teeth on top of their heads (being Chaos guys, they have shit like that). Literally. Iron Warriors are also the batshit insane sickfucks behind Daemonculaba. They're the only Chaos Space Marines who don't break down in maniacal laughter constantly, as they see this as a sign of weakness. They're not terribly fond of Daemons like the Word Bearers or the Black Legion are, though they will make use of them unlike the Night Lords who don't even like Chaos and they aren't closet loyalists like the Alpha legion. Many of Black Library's authors are quite fond of them for being more "realistic" and "gritty" (total bullshyte) than the other traitor legions and they are one of the most frequently appearing Chaos Space Marine Legions. But they haven't been in so much as one video game, so hah. (Actually they've been in the entire Dawn of War 1 serie as a Chaos faction, they just weren't in the campaign).

They used to be incredibly badass with special rules for having more heavy weapon options including tanks and artillery but Gav Thorpe (who's basically Matt Ward's husband) decided that spikey marines should be inferior to loyalists in every way possible.