The Imperial Hounds are a 21st (Cursed) founding, roughly Codex compliant, Space Marine Chapter. They were created with experimental Gene-Seed that was heavily modified and may have had more gene-seed organs implanted that were crafted by the Mechanicus' Magos. Their exact linage is only known to the long dead magos who created them and the highest officers of the Inquisition. (though most sources point to Iron Hands proginators)