For some reason, the King_(Tekken) Tag was completely removed and all instances were replaced with the Guin tag which is utterly wrong, especially when you keep the Namco and Tekken tags. So, let me try to spell this out thoroughly.

Guin is a Warrior who's head is that of a leopard. His head is real, and he can express with it, including closing his mouth. As he is a warrior, his attire is one that old movies and shows normally would showcase. Mainly, he wears a black loincloth and a leather harness, wielding a sword. Also, because his head is real, you can see it connect with the body. His fur covers all the way to the shoulders and he has black spots on his skin. He does not have a tail.

http://0-media-cdn.foolz.us/ffuuka/board/a/image/1339/90/1339904123067.jpg

http://i888.photobucket.com/albums/ac81/Manga4life1/GuinSaga2.jpg

http://sharetv.org/images/guin_saga_jp-show.jpg

http://i8.mangareader.net/guin-saga/1/guin-saga-1824229.jpg

King, from Tekken, is a Luchador who wears a mask. His head is fake and shows no expression (however, artists tend to ignore that) and his mouth is always open. As a mexican wrestler, he wears a fitting attire. Elbow pads, kneepads, trunks, or tights mainly cover his body and mostly have his name adorned on them. Because he is wearing a mask, it only covers down to his neck and you may see hair growing out of it. His skin has no fur but he does have a fake tail.

http://www.hdwallpapers.in/walls/king_tekken-wide.jpg

http://www.game-art-hq.com/wp-content/uploads/2011/06/Tekken-4-King-Render.jpg

http://images.wikia.com/tekken/en/images/4/49/King.jpg

http://images.wikia.com/tekken/en/images/c/c4/Tap_king_stand.jpg

There is a third character, but oddly enough people don't get him mixed up. That's Armor King, who is also not King.

http://www.todofondosdejuegos.com/wp-content/uploads/images/todofondosdejuegos-com_tekken%205:%20dark%20resurrection-26.jpg

The main differences to look for are attire and whether the head is real or not. Basically, if the character is wearing modern clothes or wrestling attire, it's king. If he is wearing a warrior's garb or simply a loincloth it's Guin.

Seirya seems to be your culprit. That user also seems to be really into gay muscle considering their tagging history.
https://e621.net/user/show/90603

They also have a crap ton of tag edits for a normal Member level user.

Well it is just situational and if he is not wearing his clothing, someone could mistake king_(tekken) for Guin if they aren't looking for the differences around the neck.