Szass Tam is the current leader of the nation of Thay, in fact if not in name. While he retains the title of Zulkir of necromancy, he is also the current ruler of Thaymount, and is generally considered the most powerful of the Red Wizards currently in Faerun.
Szass Tam seized control of Thay and became a lich shortly afterwards, and rumour has it that he wishes one day to ascent to godhood. Many believe that the current state of Thay – largely lifeless and inhabited by the undead – is a result of a failed ritual that Tam had hoped would make him into a god. Tam has neither confirmed nor denied this, perhaps because most fear to ask.
Tam is feared in large part because noone knows his whereabouts much of the time; it is rumoured that he often walks among his people in disguise, and several popular uprisings and plots by the Thayan resistance have been foiled by information Tam should not have been able to possess. Whether this is the work of Tam personally or his elaborate network of secret police is unknown.