Board Thread:Fun and Games/@comment-27912807-20170428183448/@comment-25101089-20170428190645

Tolkien never made his mind up on this definitively. His original idea was that they were corrupted Elves, as the published Silmarillion states, but he later discarded this because it implied that Evil was able to change the eternal fate of immortal Elves into mortal Orcs, which is philosophically problematic given the limitations of what Evil can accomplish in his world.

Some later ideas he considered were having Orcs be corrupted Men, or fallen Maiar in Orc-form (like Balrogs). The idea of corrupted Men is not consistent with the timeline of the Silmarillion. While he did attempt to revise much of the mythology in his later years, including the timeline, he never managed to do so to a satisfactory state.

When Christopher Tolkien compiled the published Silmarillion from unfinished notes and contradictory passages, he decided to go with the 'corrupted Elves' solution because he deemed it the least problematic. So there isn't a 'real' answer to this, as is the case with many things in the legendarium.

What do I think? Not as the mod creator, but just another fan of LotR? None of the ideas seem really satisfying, but having Orcs be corrupted Maiar is the one I like least. It feels completely wrong. And given the timeline we've got, they can't have originally been Men either - although some of the later ones could be.