Individuals listed by company and relative rank as of the events in medias res, after the events of Horus Rising and midway through False Gods.
Spoilers to both works below:

Equestrians:

Celestia- Princess of the Day, co-ruler of Equestria

Luna- Princess of the Night, co-ruler of Equestria

Twilight Sparkle- Princess of Friendship

Starlight Glimmer- Pupil of Twilight Sparkle

Northling Barnyard- Doctor, University of Canterlot Medical department

Moondancer- Graduate Student, University of Canterlot Thaumatological department

Sunset Shimmer- Former pupil of the Equestrian crown

Trixie Lulamoon-Stage performer

Legiones Astartes:

XVI legion: Sons of Horus
Horus Lupercal- Primarch of the 16^th Legion, Warmaster of the Great Crusade
Genetically crafted 'son' of the Master of Mankind. “First among equals” of the primarchs. Mortally wounded by the poisoned Anatheme blade during the assault on the moon of Davin.

Maloghurst “The Twisted”- Equerry to the Warmaster and senior diplomat

Timmult Vaddon- Chief Apothecary
Recovered Horus on the moon of Davin, currently in possession of the Anatheme blade for the purposes of study.

Ezekyle Abaddon- First Captain, 1^st company
Member of the Warmaster's Mourneval advisory council. Most senior commander under Horus Lupercal, and leader of the Warmaster's Justarian guard. Member of the Warrior Lodge.

Kalus Ekaddon- Catulan Reaver Captain, 1^st company

Tarik Torgaddon- Captain, 2^nd company
Member of the Warmaster's Mourneval advisory council. Accompanied Garviel Loken in the recovery of the Anatheme blade. Member of the Warrior Lodge.

Horus Aximand “Little Horus”- Captain, 5^th company
Member of the Warmaster's Mourneval advisory council. Member of the Warrior Lodge.

Yade Durso- Lieutenant, 5^th company

Serghar Targost- Captain, 7^th company
Official speaker and leader of the Warrior Lodge.

Garviel Loken- Captain, 10^th company
Member of the Warmaster's Mourneval advisory council. Recovered the poisoned Anatheme blade.

Nero Vipus- Sergeant, 10^th company

Luc Sedirae- Captain, 13^th company
Warrior Lodge's gatekeeper.

Tybalt Marr “The Either”- Captain, 18^th company
Accompanied Garviel Loken in the recovery of the Anatheme blade.

Verelum Moy “The Or”- Captain, 19^th company
Slain by Eugen Temba during the assault on the moon of Davin.

XVII legion: Word Bearers
Erebus- First Chaplain of the 17^th legion
Spiritual leader and founder of the Warrior Lodge, current guest of the 16^th legion. Stole the Kinebrech Anatheme blade and corrupted Eugen Temba.

Kal Belekar- Captain, 94^th company

XX Legion: Alpha Legion
Alpharius- Twin- Primarch of the 20^th legion

Alpharius Omegon- Master of the Effrit, Twin-Primarch of the 20^th legion

Non-Astartes
Hektor Varvarus- Commander of the 63^rd expedition fleet

Ing Mae Sing- Chief Astropath, 63^rd expedition fleet

Eugen Temba- Former Governor of Davin
Corrupted, then persuaded to assassinate Horus Lupercal on the moon of Davin with the Anethame blade.

Ashkub- Davinite Delphos High Priestess

Sabinius “Strider”- Asset of the 20^th legion
Young dream strider mystic of the Manataxii tribe.