Horus wasn’t the only one at the time to turn heretic. He had others with him. And soon, they can join him on the battlefields of The Horus Heresy as Games Workshop shows off the Esoteris Consul.
From the article:
Horus’ fateful encounter with the Ruinous Powers at the Serpent Lodge on Davin turned the Warmaster traitor, but he wasn’t the only member of the Legiones Astartes to dabble with the darker forces underpinning the galaxy.
With the Heresy in full swing, the Traitor Legions are free to explore the forbidden arts anew – and the Esoterist Consul steps out from the shadows.
No matter how fiercely the Emperor suppressed the Primordial Truth, there were always those willing to explore the Immaterium’s secrets – whether to ward off its eldritch denizens, or harness their unnatural power.
The Traitors quickly embraced these mind-expanding secrets, spread by robed conjurers through the rituals of the Warrior Lodges – but as the Heresy progressed, even Loyalist psykers drank deep from wells of outlawed knowledge. Desperate to overcome the Warmaster’s strange new powers, gifted lore-seekers and ex-Librarians defied the Edicts of Nikaea – with or without the blessings of their Primarchs.