I wrote a research essay for English class. We had to do it in MLA format and I already did that. I'm just stuck on one citation. On the front of the book(and the back) there's an author's name (A doctor) and then there's a consultant(also a doctor). Do I need to put the consultants name in the citation or just the author? The consultant is an author also but just for this book, he was a consultant I think.

I've also looked online but it's not helping me.