Luigi.

Mario's younger brother. Period.

That's what most people can say about him. But Luigi doesn't care.

He follow Mario around and does whatever Mario does, better or worse (usually the later one).

But the world is cruel, his popularity (???), I mean, too many spotlights on Mario, Luigi merely lives in his shadow.

Luigi is not a sad character, because no matter how much fames and fans Mario (even Wario) has steal from him, he doesn't care.

Doesn't care. When one doesn't care anymore, one becomes invincible. If you don't care about your lovers, how can she break your heart? If you don't care about the result of any game, how can you really lose? Maybe you lose, but you don't feel like losing at all, because you don't care.

Maybe Luigi does care. And maybe as a compensation for the long forgotten Luigi, Nintendo throw him a Mansion at the dawn of GC. But... like a big joke, that turns out to be a demo disk, shorter than any Mario games on N64 and SNES. Poor Luigi.

However, he is still invincible. He doesn't care.