The Warhammer 40,000 is a massive, sprawling one, with almost four decades' worth of lore and backstory. Though factions have been added over time, units are updated frequently, and the lore is fleshed out more in Codices, books, and other external media, 40K's Chaos faction has been present in some form or another since 40K's first edition, Rogue Trader, back in 1987.