I think it's stupid, but it's Mario. That's why they're called the Super Mario Bros. Mario Mario and Luigi Mario. But its a much easier name to remember than any Italian last name that I know.
Mario, I know... Stupid. I mean, Mario Mario and Luigi Mario! Really, Nintendo Mario is all wewe can cam up with for a last name!? Okay, yea it is Mario, though.. So I have heard a long time back.
They are the "Mario brothers", so wouldn't their last name be Mario?! IE: if 2 brothers are Gary and Paul Smith, they will be referred as the "Smith Brothers"…technically.
Their last names are Mario for two reasons: one, in the Super Mario Bros. Movie, Luigi alisema that his full name is Luigi Mario. two, the duo is called the Mario Bros.