I asked Azure like, how the fuck he made Deter. And this is what he told me (in my words).

He had a username on Roblox, determinedsansy. He said he was playing Jailbreak and there was this RP going on. He named himself Deter, who was a half-dragon, half-fox, half-human demon. This was before he knew about UnderTale. Deter turned into Ink, the brother of Ink Sans and Bendy. Ink turned back into Deter, when UnderTale came out. At first, Deter was just a background character with no special powers. Then Azure watched some GlitchTale AMVs and decided that Deter should have some magic. So he gave Deter an upside down DETERMINATION SOUL along with the others, including LOVE, FEAR, and HATE. Then I came along, adding small details to him. And that's how we have the Deter today.

Edit: He was called Diagon while he was in the family, because of Ink Sans. Forgot to add.