Thanatos is the God of Death, he works under Hades in the Underworld and collects souls for him.

Thanatos is believed to be a 'lazy' god according to several characters. In fact, Thanatos' work was 'sabotaged' which Thanatos is unaware of this situation. He can be a bit brash due to his position. With the arrival of Persephone interning in the Underworld corps, he's skeptical towards her and is willing to obtain any authentic info that has to do with the sabotaged of his work and the truths about Persephone. 

Episode: https://www.webtoons.com/en/romance/lore-olympus/episode-39/viewer?title_no=1320&episode_no=42