In the season one finale of Death Save, Vares and crew had a showdown with his dad. But just what Vares's dad was doing, and how he was doing it, never really came out. Turge threw a dog and any bad-guy monologue was cut off. Here's the rundown.
Arden (Vares's dad's name, in case you missed it) was never a good guy. He cut out on his one when Vares was just a little McHalf-Elven. Arden didn't get any nicer from there. He spent the intervening years looking for some way to show the world what a powerful wizard he was. Around the time Vares was learning the magics that would end up binding him to a great old one (and destroy the Goldpetal estates in the process) Arden finally began to formalize a plan to take over the world.
Step 1: Tear Down the Wall
The planar divisions of the world were pretty strong, so Arden began by weakening them. He did this just about the time Vares cast his summoning. This also resulted in old gods who had been walled off from reality by the church, reaching though the veil to find new followers. See: Castor Stone and The Sealer of the Guilty.
Step 2: Build an Army
While he was pretty tough as wizards go, no single character in a D&D game is going to be able to take on the world. So Arden used the weakened veil to draw forth beings from other planes and worlds. He then bound their essence into a rune stone. Each of these stones could be used to provide a humanoid with powers associated with the being whose essence it contained. A combination of promises and threats and magical charms got him subjects who, through the use of these stones, formed his army.
Step 3: Raise Hell!
Vares, Castor, and Turge caught Arden during the execution of Step 3. When they destroyed him the controls he had put in place to maintain all of the magics listed above were destroyed as well. The runestones were rendered (mostly) inert, the planar weakening was (mostly) repaired, and flow of power from this plane to others was (mostly) cut off. Any monsters or whatnot that had previously crossed the threshold are still in the world, making it a (mostly) more dangerous place in the aftermath.