>>64858060>The mother fucker also conquered other planets by the time the Emperor arrived, how many other Primarchs even made it off their planet before Big E showed up?
Dorn, Guilliman, and Ferrus were the only ones who did.
Macragge had spaceflight and limited trade with nearby worlds when Guilliman arrived, grew up, and made it prosperous before the Emperor showed up on the nearby world of Espandor and heard about Guilliman from traders.
Dorn uplifted a bunch of Inuit tribes and made a space empire. Arguably. It's not clear how much was him, and how much was the fact that he found and figured out how to get the DAoT ship Phalanx working (assuming it was DAoT, he refers at one point to having built/engineered it himself). But he was the emperor and warlord of a small system/subsector by the time the Emperor found him (reasonably early, he'd probably have made it further otherwise).
Ferrus made it to orbit, where Medusa had a bunch of derelict space stations that he got running again, but Ferrus wasn't really one for empire building. If he was, he'd probably have made it further.
None of the other Primarchs made it off their planet, that we know of. The Lost ones might have, but there's no data.>>64858148
It's unclear whether Phalanx was built by him or found (and repaired) by him, but he absolutely made it offworld and was ruling an empire of his own.