It is decidedly vague on whether or not the Slayer has retained any humanity. While many of the coalition's analysts who've examined him from within and without his tomb determine he is human from various blood samples of the subject that were taken and studied, one such technician notices trace amounts of exotic material in his genetic makeup that makes him decidedly something else. This is confirmed in his final battle with the Khan Maykr, who admonishes him as a once-mortal man who dared to deny her people's way of life. His ascendance to a living force of nature stems from the empowerment given by the rogue servant of Urdak known as Samur Maykr (or the Seraphim) in Doom 2016, who used his race's technology to vastly empower him.