So, we all know that Horus became Warmaster after the battle for Ullanor.

I know that Horus was the emperors favourite primarch:

For a thirty years he was the only Primarch to have been discovered. Friendship between the Emperor and Horus grew rapidly and the Emperor eventually trusted him enough to give him command of the entire force of the Imperium.


Horus flayed him alive with but a look and in that instant the Emperor realised how far his favoured son had fallen.

From the Lexicanum Article on Horus Lupercal

So, the question is not why the emperor made this decision. I am also aware that it was probably a process to decide which Primarch to make Warmaster. But what is the earliest point the Emperor mentions Horus as being the (probable) Warmaster?

  • I'm not sure this was ever mentioned prior to Ullanor, atleast not in written works
    – NinoM
    Commented Aug 11, 2020 at 13:57
  • I am pretty sure in one of the short stories Malcador talks about Horus always being destined to be warmaster, I think Robute also states that somewhere. However it has not been stated how and why the emperor made that choice.
    – Richard C
    Commented Aug 11, 2020 at 18:07

1 Answer 1


I don't believe any works have expanded on The Emperor's thought processes in any detail, and the Emperor (wisely) didn't publicly air his musings on the choice.

In "Slaves to Darkness" Horus has a flashback about talking to Malcador about his choice and what it'll mean, but this would not have been when it was first decided, or (I believe) made public. I can't remember exactly though, it's been a while.

Horus was the obvious choice in that he was the first to be reunited with the Emperor post-scattering, and thus spent the most time one-on-one with Big Daddy E. He had the respect (if not love) of most or all of the other Primarchs, and he was also both the ultimate general and a diplomat/statesman extraordinaire, a combination few of his brother Primarchs could boast of.

You are correct that the announcement happens around the time of the Ullanor campaign, with the investiture happening as part of the following Triumph.

The reason for appointing a Warmaster seems to be the Emperor deciding to focus his efforts on the "Human webway" project which kept him physically confined on Terra. He well knew that the various Primarchs - for all their superhuman abilities - were no more able to govern themselves than a group of kindergarten kids.

(obligatory "damn you Erebus!")

  • The Emperor doesn't have to announce it publicly, he might've mentioned it to Malcador, his closest confidant, way before he announced it to the primarchs. As an example, there's a short story where Mortarion refuses to accept his Legion as a Primarch as he has a problem with psykers and Malcador mentions that this issue will be handled. It was decades later that the Council of Nikaea took place.
    – Shade
    Commented May 28, 2021 at 9:56

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