In the Book Theif, Death is our guide and narrartor through the story. He in some way seems human and expresses emotions. Of course he may not actually be human but is linked to humanity.
Death is fascinated by humans and the colors of the world and often fixes on the sky at the time of each human death. He desires to find ways to give meaning to his work.
One of the main things he does is collect stories about courages humans. Liesel is particularly interesting to him because of her courage and personality. Stories like that are what keep him motivated to keep going.
He tells us at the beginning of the novel that the most painful part of his job is seeing "the survivors," "the leftover humans," "the ones who are left behind, crumbling among the jigsaw puzzle of realization, despair, and surprise" (1.20, 1.21, 1.22).
He also works to correct humans' perception of him, revealing that he does have a heart, that he doesn't carry a scythe, and that he, in fact, appears quite human. He describes how he has to do the bidding of many different bosses. Like Hitler.