The Illuminate Pact is an agreement between 7 Imperial groups, most notably, 6 different Space Marine Chapters, as well as a group of Inquisitors from an unidentified and little known Ordo Minoris. This Pact was made by this unknown Ordo for the sole purpose of combating the extreme measures utilised by the Ordo Hydra (an extremist offshoot and secret society of Inquisitors) as well as the Forces of Chaos that most Imperial forces are unaware of. These six Adeptus Astartes Chapters where chosen because they had all fought against the nefarious forces of the Ordo Hydra. Due to this unknown loyalist Ordo's secrecy within the ranks of the Holy Inquisition, it stood to reason that an external force would need to be utilised to combat their foes.