- This mystery is considered solved.
Mario and Luigi's last name has varied depending on the source.
The name "Mario Bros." has long led people to believe that both brothers have the last name "Mario". This is reflected in sources such as the 1993 Super Mario Bros. movie and the Mario Party 2 Prima Games guide. It has also been endorsed by the Mario Bros.' voice actor, Charles Martinet.
Other Nintendo employees and representatives, including franchise creator Shigeru Miyamoto, used to state that Mario and Luigi have no last name.
Miyamoto changed his stance at some point prior to the Super Mario Bros. 30th Anniversary festival in 2015. During this event, he stated that Mario and Luigi both have the last name "Mario".
Miyamoto later continued the gag in a Game Informer interview, stating that Link, main protagonist and playable character in the series The Legend of Zelda, has the last name "Link".
During the development of Donkey Kong, working names for Mario included "Mr. Video Game" or "Mr. Video". He is instead named "Jumpman" in the final game, however.
Throughout Yoshi's New Island, the adult Mario is disguised as a Warp Pipe and referred to as Mr. Pipe. While the name reflects the disguise, depending on the player's interpretation, "Pipe" could be taken seriously as another alternative last name.