The original version of the Orks, back during the War in Heaven. Modern Orks are their degenerated descendants, because every galactic power with two brain cells to rub together head shots any Ork Warboss that looks like it could be turning into a Krork and leveling what infrastructure got made.
See, Orks are basically a living RTS race, complete with a tech base that's genetically and psychically encoded into them. The more successful an Ork Waaagh is, the more of their own techbase they can unlock(and the bigger and stronger the Orks themselves become). After a few centuries to a millennia of success, an Ork Waaagh can go from zero space flight and little industry to being
scary developed across hundreds of worlds and being on the verge of constructing their own
Attack Moons and Attack Planets.
Orks are the only race that fought during the War in Heaven that could actually restore themselves to the heights they had at the time, becoming Krork once again but this is
not a good thing as Krork are still a rather monstrous race of living weapons, just with psychically boosted scary advanced technology, insanely huge
disciplined armies of
gigantic powered armored Krork(Imperial Knight sized and beyond) and the ability to speak in proper grammar.
During the Great Crusade, the main reason the Emperor pushed for such a rapid blitzkrieg of the galaxy was because the Ork Empires at Gorro and Ullanor were getting scary close to reaching the point where they snow ball beyond all control(Gorro itself was an almost complete Attack Planet), and odds are those weren't the only ones as well.