The first part of Nulgath's birthday release was last night.
According to the flashbacks the players experienced in the Nulgath Nation's base when allowed access to the library by Dirtlicker, Nulgath used to be a human who fled from the Grand Inquisitor's forces and found himself in the Fiend Realm which only a few survived the entrance to. Nulgath met Adimonde: God of Fiends who persuaded him to become his champion in a plot to conquer worlds. Nulgath planned to do that while facing off against Adimonde at some point. From there, we as Nulgath in his earlier form had to get the loyalty of the fiends ranging from the Bloodfiends, the Dreadfiends, and the Fiend Champion by fighting them.
It turned out that the Nulgath that Malgor tried to manipulate was one of his clones like the one he left behind in his lair somewhere in the Dwarfhold Mountains and the real Nulgath is still in the Oversoul reality. He ordered Dirtlicker not to waste any of his soldiers in battle or else. One of the souls from Oversoul met the players and learned about Nulgath's history. The next release will have us going after the extra Fiend Shards in order to weaken Nulgath.