From a scroll describing the realm of Thanatos, God of Death:
Thanatos was born at the dawn of time to create and hold dominion over the Underworld, the realm of souls. No spirit severed from its body can hope to escape the void that is His realm. Further, it is only through the minion Charon, under Thanatos' jurisdiction, that a soul can hope to return to life from the depths of the Underworld. Those who cross Him are rumoured to be subjected to horrendous torture behind the walls of a grim fortress. Those whom He favours, on the other hand, pass through the Underworld as nobles.
He pays little attention to the upper world, and is aloof even among the souls of His realm. As a result of this obscurity, His overriding goals remain unknown. From time to time He has actively sought the expansion of His realm through increasing the rate of death in the world. Yet other times He remains hidden away in His palace in the city of Dis. Thanatos is often perceived as a moody and brooding God, speaking rarely and tersely.
History
Much like Aesir, Thanatos was not very visible during the war between the Pantheon of Imperian and the Demon Gods. His contribution, however, was significant, as He chased Azaoz through the portal back to His home and, historians can only assume, savagely bludgeoned the Demon Lord into oblivion, literally.