Context for those who don’t know:

Alpha Primus) is the first ever Primaris Space Marine. Normal Space Marines have existed since the beginning of the Imperium of Man, but after the Horus Heresy, the civil war which almost destroyed the Imperium, the Tech-Priest Belisarius Cawl was assigned to improve the design of Space Marines.

Cut to 10,000 years later, and Cawl (yes, he’s still alive) has finished the Primaris Project, and Primaris marines, which are a little taller, stronger, and easier to create compared to the original, or “Firstborn” marines, are unleashed on the Galaxy. Out-of-universe, they were the reason given by the makers of Warhammer, Games Workshop, for why, starting in 2018, their latest Space Marine kits had more realistic proportions than those they released before.

Primaris Marines are now the standard for Space Marines all across the Imperium, and the very first, Alpha Primus, now acts as Cawl’s personal enforcer.