That's right. The King was accompanying Doktor Schmidt (remember him?) and Etelka Herzen on their mission to find the warpstone comet for the Red Crown. He was present at the ball in Nuln, being randomly menacing. Later, he was with Etelka at Castle Wittgenstein, and briefly fought Julian and Heinrich. After that, he made a few more menacing appearances but did nothing (he especially likes stalking Mortus, it seems). He was bound by the limitations set on him by his summoners.
In Altdorf, as they were being hunted down, the remaining Red Crown cultists called on the King again, and this time let him off the leash. He fought Julian and Heinrich again, being driven back by Heinrich's magical axe and then losing his connection to the mortal world. They chased the surviving cultists as they tried to flee Altdorf by river, and obtained the King's true name from Othmayer.
The King made another 'scary' appearance, and then tried invading their dreams instead. He also appeared to Mortus in a lengthy vision of the outer realms.
He's annoyed, and may be very powerful! However, Max thinks that the true name they got from Othmayer is genuine.
On cults:
The Purple Hand and the Red Crown are both cults dedicated to destroying The Empire from within. Both are dedicated to 'the Changer,' and seem to hate each other more than anything else. The Red Crown (based in Altdorf) has been destroyed, apart from Etelka Herzen (who ran away after failing once too often) and the King.
The Purple Hand are supposed to be based in Middenheim. So far, the group haven't met many of them: there was the dead Kastor Liebenrung (the one with the fake inheritance), and a nameless chaos warrior who seemed to be a guest at Castle Wittgenstein.
The business in Bogenhafen, by the way, did not involve a chaos cult: Teugen was a demonologist, and knew Schmidt and Herzen, but was not a member of the Red Crown. His plan was purely to evade a bargain he'd made with a demon by sacrificing his followers in his place (though the demon had tricked him, and the ritual would have done something very nasty indeed).
Other cults that have been mentioned: the Jade Septre, and the Ordo Ultima. Both sex/drugs cults. Not interested in anything other than corrupting people for fun.
