They aren't really Mario bros
Here's an interesting bit of trivia - Super Mario's creator Shigeru Miyamoto spoke in a recent interview and said Mario and Luigi don't have last names. This comes after decades of people insisting they are called Mario Mario and Luigi Mario, which is silly when you think about it.
"This is an old story, but Hollywood did a film version of the Mario Bros. many years back [don't remind us -ed]. There was a scene in the script where they needed a last name for the characters. Somebody suggested that, because they were the Mario Bros., their last name should be Mario. So, they made him "Mario Mario". I heard this and laughed rather loudly. Of course, this was ultimately included in the film. Based on the film, that's how their names ended up. But, just like Mickey Mouse doesn't really have a last name, Mario is really just Mario and Luigi is really just Luigi." - Shigeru Miyamoto
So that's the end of that.
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