Vecna

Vecna, the Keeper of Secrets and the Immortal Necromancer, is an archlich who ascended to godhood. His portfolio includes secrets and undead. He rose to power during the Mythic Era before being betrayed by his top lieutenant, a vampire named Kas. This legend is told in the tale of Kas the Betrayer.
Typical worshippers of Vecna are necromancers, trickery clerics, and other liches. His symbol is a hand holding an eye. Although Vecna is an official part of the Eastern Pantheon, there are no grand temples built in his honor. However, there are more people who occasionally send the archlich a prayer or ask him for a favor than is casually admitted. After all, who wouldn't want to have someone to tell their deepest, darkest secrets to? Especially if they knew that he would cover those secrets forever. It's rumored that in every major settlement on Polnarus, there's a secret, hidden shrine devoted to this dark deity.