Here is my favorite (and JKR’s one of her favorites) theory here it goes:

Dumbledore is Death

In the Deathly Hallows, we hear a story within a story: “The Tale of the Three Brothers,” centered on the myth of the Peverell siblings. In the tale, each of the three magical brothers attempts to cheat Death of his due in various ways. Many fans have compared each of the three brothers to the story arcs of Voldemort, Snape, and Harry. Voldemort echoes the story of the eldest brother, who believes he can defeat Death with massive magical power but eventually fails because of his own hubris. Snape represents the middle brother, who is consumed by his grief over a lost love, Lily Potter. Finally, the youngest brother is a representation of Harry, who manages to hide from Death for a long time before willingly going with him and embracing his own demise. In many ways, Dumbledore can be seen as representing Death from the fable. He possessed all three Deathly Hallows at one point, gave Harry the invisibility cloak of the youngest Peverell brother, was at least partially responsible for the demise of both Voldemort and Snape, and is the character who greets Harry when he “dies” and goes to King’s Cross station. While we’ll probably never get an actual confirmation of the theory, Rowling herself has gone so far as to say that it is her favorite theory of all time and that “It’s a beautiful theory and it fits.”

Stay safe!!