Mario, Luigi, Wario, and Waluigi are all voiced by the same guy
We wish we had the kind of job security of Charles Martinet. Ever since Super Mario 64 the actor has been Mario's voice in virtually every game he's appeared in since. But he isn't limited to Mario, as he does voices for all the alternate versions of the Italian, including Luigi, Wario, Waluigi, and the Baby versions of said characters.
Donkey Kong was originally a Popeye game
Back in the early 1980s, a young Shigeru Miyamoto was working on his first game, one featuring cartoon character Popeye climbing up scaffolding to save Olive Oyl from Bluto. Unfortunately, Nintendo had just lost the rights to make games based on Popeye, so Miyamoto and his team hand to think of something else. They replaced Bluto with a gorilla, Olive with Pauline, spinach with a hammer, and Popeye with Mario, and the rest is history.
Kuribo is the Japanese name for Goombas
When we first heard that the highly desirable footwear power-up in Mario 3 was Kuribo's Shoe, we were perplexed. We later found out the green shoe was named after its occupant, the Kuribo, which is the Japanese name for Goombas. In remakes of SMB3 the name has been switched Goomba's Shoe, though they're still known as Kuribos in Japan.
In Mario Golf, Luigi does sign language for "lesbian"
Probably without intending to, Mario Golf taught many a word of American Sign Language. After sinking a birdie, Luigi makes an "L" with his thumb and forefinger while striking a pose. Turns out that in ASL, that means "Lesbian." Look, we're just relaying this, without comment.
The first Mario Triple Jump was in Donkey Kong for Game Boy
Ever since Mario moved into the third dimension, the triple jump has been one of his best attributes, used by more skilled Mario players to quickly clear a stage. But the ability actually made its first appearance in a 2D game: 1994s Donkey Kong for Game Boy. You start from a handstand and after carefully executing a couple well-timed jumps he can achieve heights formerly unreachable. Mario even sticks his hands out in celebration after the third jump, just like he does in Super Mario 64, so clearly Miyamotos team was inspired by it.
The grass and clouds in Super Mario Bros are the same
This spread around the internet a couple years ago, so maybe you heard of this, but do you know why it's the same? According to Mario development veteran Takeshi Tezuka, it was because the game could only hold 256 unique elements, so for the sake of space, they had to double up.
Princess Peach was once Princess Toadstool
Much like Bowser/King Koopa, Peach has a name she's left behind. She's always been Peach in Japan, but in the US she was Princess Toadstool in older titles. She permanently changed to Peach in Super Mario 64, though she was first called Princess Peach in English in the forgotten SNES title Yoshi's Safari.
The ending to Donkey Kong for Game Boy connects it to Super Mario Bros
If you never played the Donkey Kong for the original Game Boy, download the Virtual Console version to you 3DS this instant. If you finish all 100 levels of the ingenious puzzle-platformer, you'll see an ending that that cleverly connects it to both Donkey Kong Junior and Super Mario Bros. Complete the title to see it for yourself.
Diddy Kong originally designed to be Donkey Kong Jr
The Donkey Kong series had been pretty quiet until Rare took it over in the early 90s with Donkey Kong Country. When Rare was first designing the game, the plan was for Donkey Kong to be accompanied by a second player as Donkey Kong Junior. But Nintendo felt Rares redesign for the ape was too extreme. Given the choice, Rare kept the redesign and renamed him Diddy Kong.
Super Mario Bros 2's ending is foreshadowed from the beginning
After plugging the NES cartridge for Super Mario Bros 2, we were confused by how different it was from the last Mario title, with weird new enemies and physics. We now know that's because it was a reskinned, non-Mario title, but the in-game reasoning was that it all took place in Mario's mind, which most people could tell ahead of time if they bothered to read the instruction manual. The game takes place in Subcon, short for Mario's subconscious.