Harry Potter is the only known Master of Death, having gathered and mastered all three Hallows and most importantly, accepted death, as the true master understands that death is inevitable and that there are worse things in life than dying. He did not unite all three of them physically at the same moment, as he possessed no more than two at the same time. Albus Dumbledore had also gathered all three, though physically owning no more than two at the same time, and did not master the usage of the Cloak, but he could qualify for the title of the Master of Death as he fulfilled the most important criteria needed by accepting death. With the Stone lost, it is unlikely there will ever be another to hold the title.

Thank you for reading my book, and remember, "Magic can be found in the darkest of times if one remembers to turn on the light" - Albus Dumbledore