Primaris Ancient
Primaris Marines dubbed honorable enough to have the privilege of carrying the Standard's Banner. Identifiable by their white helmets (Although that could change depending on the Chapter), they are in no way related to another dude-clad-in-powerarmor-wearing-a-white-helmet-that-also-comes-with-the-same-name-from-a-certain-WH40K-game. In case you were wondering, "Ancient" is a old corruption of the rank of "Ensign" which was a term for an army's flagbearer in the Middle Ages, so it has nothing to do with how old the Marine in question actually is, that said, since you have to earn enough honor to hold the standard, these guys are likely somewhat ancient.