Most powerful Beings in the Forgotten Realms?

Here are some alternatives of whhich creatures i think is on top of the food chain in the forgotten realms.
Do you have any specific characters or creatures to add?

Creatures from any ruleset 2.0 to 3.5 are welcome.

Creature Types:

Balor's
Solar's
Tarrasque
Titan's
Leviathan
Dragon's
Pit Fiend's
Liche's
Beholder's - added by Sylvus_MoonbowSuccubus
Succubus - added by Zeratul (cuz their hot...)


Specific Characters:

Elminster
Gromph - Archmage of the underdark
Demogorgon - Prince of Demons - added by doppleganger95
Larloch - Shadow King - Added by Lapa
Khelben "Blackstaff" Arunsun - Lord Mage of Waterdeep - added by Aosaw