Thanatos

The Greek personification of death. Often mentioned, rarely seen. He is one of the Titans that personify concepts, born to Nyx (night) and Erebos (darkness).

He is said to be the god of peaceful death, with Keres being the god of violent death, however, he is still thought to be merciless and hateful to both gods and mortals.

Thanatos was once outwitted by the King Sisyphus (this was before he pushed the boulder up the hill in the underworld). Sisyphus betrayed Zeus, who then ordered Thanatos to chain him in Tartarus. (Even though that was Hermes' job, but Thanatos went along with it.) Sisyphus asked Thanatos to show him how the chains worked, and Thanatos, for some reason, demonstrated them on himself. Sisyphus locked him in and fled, which earned him a bad grounding. While Thanatos was chained, no one on earth could die, and Ares was super tired of starting wars where nobody would ever die, so he went down and freed Thanatos. Once Sisyphus was back in the underworld, he begged Persephone to let him go just for a while, because his wife hadn't given him a proper burial. Persephone is tough as heck, but also very understanding, so she let him go. He went and yelled at his wife, but when the time came for him to return to Tartarus, he refused. Hermes found him and dragged him by the gosh dang ear, and this time, when he was brought back to the underworld, he was given the punishment of having to roll a boulder up a hill, just to have it fall back down when he was near the peak.
Thanatos just kind of went back to work.