Board Thread:Questions and Answers/@comment-26091443-20160702065117/@comment-26091443-20160704221726

Amarthijel wrote: I guess Gowther has been a Doll until the moment when he was somehow betrayed - which led him to join the demon clan and the ten commandmends and becoming a demon. (as Gloxonia and Dolor)

At some point he must have lost his emotions, maybe someone took them, which then led him to leave the ten commandmends and the demon clan. Since demons are a race with high emotional characters (though they're negative), Gowther was not able to stay a demon without them. That's when he became a Doll once more.

I've got the theory that every race can join the demon clan and become a demon somewhen in their lives, if their negative emotions get too strong upon themselves. Which means if you are fulfilled with hatred and betrayal and your whole life fells apart, you will be full of madness and anger and become a demon after some time :) That would explain how Gloxonia and Dolor could've become demons as well.

EDIT: ah I just thought of the fact that Meliodas can change between his demon-side and his human-side. It also relates on his emotional balance, as he has green eyes and is "human" when he's joyful and happy and gets his demon mark in moments where he suffers under a lot of negative emotions :)

tell me what you think about that :D We know for a fact that other races can become demons, this is not indispute, we've seen it happen. The thing is "doll" isn't a race.

Not really important, but Meliodas doesn't have a "human side", he's not human at all. I would think all the theories about him being half human or whatever would be done the story has pretty firmly established that's not the case. We've seen from Fraudrin and Estarossa that hiding his mark and eyes isn't even unique to him.

But that's off topic.