Since he was introduced to the world in Mario Tennis seventeen years ago, Waluigi has remained the Mushroom Kingdom’s man of mystery. 
Even though he’s starred in more than 40 (!!!) video games, we know tantalisingly little about the Bad Purple Man, so we’re weaving together the stray threads of his character into a patchwork of a man.
Waluigi, This Is Your Life.
We first met Waluigi on the tennis court as a doubles partner to Wario, Mario’s dopplegänger. We learn little else, though in the ttitle sequence for Mario Tennis, it’s clear that Luigi and Waluigi detest each other. Not even the Nintendo 64’s low-pixel count can hide the utter contempt seen at 1.29-1.45:
So it feels safe to call Waluigi Wario’s brother, right? Or has he just copied his style to create an army of two against the Mario brothers? Has he created his image in contempt against Luigi, given that its the only thing we know about him?
It’s all too cloudy. We’ve got to return to the facts. What we do know is that Wario needed a partner for doubles in Mario Tennis, so Waluigi was created by Camelot designer Fukihide Aoki – a non-Nintendo employee. He is an outsider, even in birth. 
Add to that the fact that we met Baby Wario in Yoshi’s Island DS, but not Baby Waluigi, and it’s all looking very suspicious. In fact, we have never met Baby Waluigi, which suggests Waluigi was never a baby. He simply exists – a fact neither confirmed nor denied by his bio in Super Smash Bros. Melee:
Even Charles Martinet, the voice of Waluigi (and Mario, Luigi and heaps more Mario characters, but who cares rn), has weighed in. In a 2008 interview with Kombu, he said, “I don’t know if [Wario and Waluigi] are brothers or not. I don’t think so. I think they’re just two nice, evil guys who found each other.”
While that sentence has enough fodder for a thousand fan-fictions, I’m hesitant to say they’re gay. Waluigi is always flirting with Princess Daisy, though admittedly that could be a cover. He’s known to overcompensate for his sexuality:
Charles also offers a rare insight into Waluigi’s psyche in that same interview, saying that while “[Wario’s] cornerstone emotion is jealousy”, Waluigi’s is “self-pity” .
But from where does the pity come? Perhaps it’s because he’s never had his own game, though fans once made Psycho Waluigi, his own unofficial adventure. 
Regardless, Waluigi should be proud of himself. From his 40+ game appearances, we know he’s an accomplished sportsman – he boxes and go-karts, as well as plays soccer, tennis, golf, baseball, Olympic sports and basketball. Impressive. He also holds some serious coin: in Mario Party III, we learn he has his own island.
Interesting design choices, but still, you know, an island. 
Waluigi is like an enigma wrapped in a riddle wrapped in a vest. We know so much yet so little. 
In a final attempt for answers, we turn towards his name, which at first just reads as a portmanteau of ‘Wario’ and ‘Luigi’. But in Japanese, Waluigi translates as ‘bad Luigi’ and it is an anagram for Iiiwaru, meaning “ill-tempered” or “cruel”. He is the Bad Luigi, an evil spirit conjured by an outside force. 
Sound familiar?
And it feels so good to be bad.
Image: Nintendo/Mario Tennis: Ultra Smash