He or "it" is not real. Merely the auditory and visual hallucinations that haunt Ori starting mid season 1. Slowly worsening overtime till it starts to eat away at that hopeful and playful demeanor he holds so tightly.

The way this is portrayed in some scenarios is far from the theme Humanity's King shows. Sometimes being shown in an animatic scenario to truly portray the horror it is and the weight of it all.

It has a scratchy voice, almost always dull and lifeless. Making the very few times it may speak with emotion memorable

Still human it may be, it's mannerism is what truly haunts.

You do not have to lower your voice or try and sound ominous at all. Again, it's only human. The portrayal wants it to seem as human as possible, enough to believe that this voice is just any other guy. While the character is seeing it as the opposite. A monster.