Prior to the Horus Heresy Fabius Bile was the chief Apothecary of the Emperor's Children. He began to secretly experiment in ways to alter the geneseed at the instruction of the primarch Fulgrim with the intention of making the legion "more perfect". These experiments led to the first examples of Noise Marines among other things.

Bile is a Chaos Space Marine and was once the Lieutenant Commander of the Emperor's Children, accompanying them to the Battle of Terra. While there he didn't take part in the main battles on the planet, rather he performed horrific experiments on the population of the world and managed to create special drugs to make the Emperor's Children more succeptable to extreme stimulation, much as Slaanesh demands. He himself did not follow Slaanesh and distanced himself from his legion and instead devoted himself to reseach into the forbidden technology of the creation of Space Marines.