 Between the late–1980s introduction of the Horus Heresy and the start of this series publication in 2006, Games Workshop and affiliates released -branded products that expanded the concept's standing as "Warhammer 40,000" background material.The release of such works, which include literature independent of this series, continued ; the works may relate to it as prequels, sequels, or expansions of its stories.Pre-series Horus Heresy literature and other related works may have been superseded or rendered obsolete, while other similar material may no longer be authoritative even as it remains in Horus Heresy and "Warhammer 40,000" canons; still other non-series Horus Heresy material has been eventually incorporated into the work.