Sanguinius

Sure, they’ve said it’s a 40K show. But what if… it was a 30K show instead? The time period of the Horus Heresy—a massive civil war among the chapters of the Space Marines when the titular Horus, the God-Emperor’s most beloved son, is corrupted by the evils of Chaos—is a vast one, ripe for storytelling, and studios love an origin story.
But why Sanguinius instead of Horus? The leader of the Blood Angels Space Marines, Sanguinius is known for two things: having giant angel wings, and dying horribly at Horus’ hands at the climax of the Heresy. Gives Cavill an eventual way out, at least.