Board Thread:Warhammer 40k General Discussion/@comment-25618639-20141206200938/@comment-24944355-20141207092648

As I said the other primarchs roles were hard to figure out - the Lion was so secretive that we can't know him well enough to tell & the same goes for the Khan & Mortarion, Angron was so twisted & brutalized by his implants that anything other than the beast is lost. Vulkan's Role may have has something to do with the forge but again we know too little of him to know for sure. As for Dorn about the only thing I could think of is head of the custodians, which leaves us with Magnus & Corax who each may have been destined to be some sort of scholar but we lack enough information to be certain for them as well.

Whatever their roles were to be the idea of the Emperor being arrogant enough to try to encode their roles into the primarchs genes is a likely one. Even if Chaos hadn't stolen them & scattered them throughout the galaxy to be raised very differently than the Emperor intended it's unlikely the primarchs would have fitted into the slots prepared for them as easily as the Emperor imagined.