Warhammer 40,000 is a science-fiction franchise and tabletop wargame created by Games Workshop. The franchise serves as the setting for If The Emperor Had a Text-To-Speech Device, drawing from decades of lore in both game manuals and published novels, as well as creating its own interpretation of said lore.
This wiki only provides cursory knowledge about the franchise to help understand the story; for more comprehensive information, please consult a dedicated wiki such as Warhammer40K, Lexicanum, or 1d4chan.
For a very general overview of the setting, the Emperor himself tells its history in Episode 16: Universal History with Professor Emperor, and Episode 17: Emperor's Excellent Autobiography.
There is also a video introducing the setting created by TTS cast member Garrot, shown below
The tabletop game is centered around various factions fighting for supremacy of the galaxy. Said factions are: