Death

Death is one of the entities in the universe.

History
The walls of the Temple Vault on Morag displayed the four entities that criated the Infinity Stones: Entropy, Infinity, Death and Eternity. After Loki's defeat in the War for Earth, The Other told Thanos that humanity was not as weak as they had predicted and battling them is "to court Death," to which Thanos smiled.

Trivia

 * In the comics, Thanos is obsessed with Death, to the point that he once obliterated half the universe to appease her.