Warhammer 40,000 is a miniature wargame produced by Games Workshop. It is the most popular miniature wargame in the world, and is particularly popular in the United Kingdom. The first edition of the rulebook was published in September 1987, and the 10th and current edition was released in June 2023.

The Horus Heresy, also known as the Age of Darkness, was the first and most devastating civil war in Imperial history. Occurring in early M31 and lasting several years, it divided and nearly destroyed the fledgling Imperium.

Most disturbing for Horus, he was told that the Emperor had used the powers of the Warp to create the Primarchs. Horus was shown a vision of the past where all the Primarchs, himself included, were scattered across the Galaxy into a warp vortex.