For Harry Potter fans, the world is full of theories and readings that attempt to flesh the series and its characters out even beyond the wonder of everything that J.K. Rowling explicitly told us.
One theory that's been around since the publication of the final book pinpoints Harry, Snape, and Voldemort as modern allegories to the Peverell brothers we meet in "The Tale of the Three Brothers" in Deathly Hallows.
Voldemort is associated with the oldest brother, who sought power and the ability to conquer death — until his own hubris led to his end.
Snape bears commonality with the middle brother, who spends much of his life clinging to the memory of a lost love until he eventually dies for said memory.
And Harry's journey resembles the youngest son, whom Death sought for many years but could never find until the son walked willingly to him, greeted by Death "as an old friend." He "went with him gladly, and, equals, they departed this life."
So where does Dumbledore fall into all of this?
According to Tumblr user harryjxmespotter, he's the old friend — Death himself.