I know this isn't the answer you are looking for - but I would say Ettore Boiardi otherwise known as Chef Boyardee.
Face it - most Americans aren't going to be aware of any famous chefs unless they are on TV. If you are in the industry- then you know a lot of them and who is who and where they work. But for average Americans - Chef Boyardee is it.
BTW - he was a real person and helped popularize Italian cooking in America back in the 1920 - up until then it was pretty much unheard of unless you were an Italian immigrant.