Lupus The Wolf Disease An Easy Latin Question: What Is The Difference Between Lupis And Lupus?

An easy Latin question: what is the difference between lupis and lupus? - lupus the wolf disease

This is due to the use of Lupis vs lupus, as the name of a man not related to the reference to the disease lupus related. I know that lupus is the direct translation of a wolf, but sometimes I see it as a variant of Lupis and want to know the difference between the two. I am not an expert in Latin, and I quote only a character in a book, thank you very much!