XGaster he had attempted to create a new creature, something that would meet his expectations enough to have its own name and body. Unlike his other experiments He had created something that looked like a human, which bothered Frisk a lot.

"Stand up now"

Frisk had been tasked with teaching you what was necessary despite how unpleasant it might seem to have to deal with another of Gaster's experiments in that fake world he had created.