Suggestions by @mirrors55

Jack O'Connell

as Robute Guilliman in The Horus Heresy (Warhammer 40k)

Oscar Isaac

as Magnus the Red in The Horus Heresy (Warhammer 40k)

Ralph Fiennes

as Lorgar in The Horus Heresy (Warhammer 40k)

Mads Mikkelsen

as Konrad Curze in The Horus Heresy (Warhammer 40k)

Gustaf Skarsgård

as Leman Russ in The Horus Heresy (Warhammer 40k)

Tadanobu Asano

as Jaghatai Khan in The Horus Heresy (Warhammer 40k)

Jeremy Irons

as Mortarion in The Horus Heresy (Warhammer 40k)

Ray Winstone

as Perturabo in The Horus Heresy (Warhammer 40k)

Zahn McClarnon

as Corvus Corax in The Horus Heresy (Warhammer 40k)

Sam Reid

as Sanguinius in The Horus Heresy (Warhammer 40k)

Djimon Hounsou

as Vulkan in The Horus Heresy (Warhammer 40k)

Josh Brolin

as Ferrus Manus in The Horus Heresy (Warhammer 40k)

Anton Lesser

as Malcador the Sigillite in The Horus Heresy (Warhammer 40k)

Mark Strong

as Horus Lupercal in The Horus Heresy (Warhammer 40k)