During the Time of Troubles Cyric, along with Midnight (who became the new Mystra) and Kelemvor (who eventually assumed God of the Dead from Cyric), adventured and tried to locate the Tablets of Fates. The Tablets were stolen by a coalition of Bane, Mask, Myrkul, and Bhaal who sought to kill the other gods. Ao, an entity more powerful than the gods, banished all gods to mortal avatars to locate the Tablets.
Cyric found a sword called Godslayer that was a Life-Stealing sword. Using it he managed to kill several of the Avatars, and by finding the Tablets he took over ALL of those evil Portfolios, escept for Mask's. And imprisoned Kelemvor's soul, who was Midnight's lover.
With time Mystra (Midnight) helped Kelemvor escape and face the God Cyric. At the end of the battle Kelemvor won and assumed the Portfolio of Death. This is thanks only to a madness that had befallen Cyric. Cyric was banished to the plane of Pandemoniom.
By current Realms-Time (which is several years after the BG saga) Bane himself has returned and taken back his Portfolio of Strife and Tyranny from Cyric. Bane's situation was similar to Bhaal's in that he had a spawn that served as the catalyst for his ressurection. The difference between Bhaal and Bane is that Bane's plan worked.
Currently Cyric is the God of Lies, Deceit, Illusions (Taken from another God he killed), and Murder.
A god's power is defined by his Portfolio, and losing Murder would make him a weak god. That is why he doesn't want the PC to take it from him.
You know what...I am pathetic for knowing all this.
