They themselfs were not on OoT but their mask was. In Mm you encounter 2 Keatons, one on Milk Road and the other in North Clock Town.

I doubt they were goddesses or created the magical items or the temples. I think they are just an extreamly rare race that like to quiz poeple. Although maybe they are the ones who made all the puzzles? The people who built the Temples may have consulted Keatons on how to protect their items.

So maybe htey did play a part in creating the temples.

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[original looks better, but the site wont allow its awsomeness, so i had to shrink it a bit]