The Order of Cade
Acerak is a uber powerful demi lich that could easily wipe out the entire Order. Luckily, Acerak tends to play for long term gains and as an undead he has plenty of time. Thus far the Order has only managed to raise his ire a few times and they generally operate under the idea that the less attention Acerak gives them the better.
Acerak has the longest history with the Order, mostly thanks to some time travel.
Tomb of Horrors Saga
Acerak recruits the heroes that had invaded his tomb to serve him. They were much more open to the idea after falling into a trap that made evil in nature.
Revenge of the Giants
Our heroes go back in time to meet a still living Acerak. With a firm plan of not mentioning their names they arrive in his home. After killing a number of his minions they confront him, only to come to the conclusion that he was the sort best bargained with rather than being killed by. He allows them to return home, but not before someone slips up and mentions Klokworkk by name. As they travel back through time, they can’t help but noticing Acerak staring intently at their time travel ritual.