It's hard to imagine someone NOT knowing the background behind Luigi, but hey why not. WHY BREAK TRADITION NOW.

Luigi began as Mario's alternate. He looked exactly the same, except with da variation in color, the familiar green attire he wears today. This continued until Super Mario Brothers 2, where Luigi finally gained a personality of his own, becoming taller and lankier. God could he jump.

Anyway, sadly, back in Super Mario Brothers 3 and Super Mario World, Luigi returned to being a copy of Mario with different colors (cept fer da end of SMW, Luigi was shown bein his normal tall tall self. ).

Otherwise, Luigi has always been da second Mario brother, sometimes not even showin up at all (Super Mario RPG (kinda) and Super Mario 64, fer example). He did star in his own game, Mario is Missing, where he was da hero, altho he STILL essentially was a copy of Mario. It wasn't until Luigi's Mansion that he ever got a game to himself and screw you all, I liked that game. BIG SURPRISE. But anyway.

He makes occasional guest appearances at times or is a secret character (Super Smash Brothers) but has never really been in the limelight... not that he really seems to mind.

Luigi is taller and thinner than his older brother, Mario, and, or so it says in da Mario Party manual, is smarter as well. On the whole, however, Luigi seems more introverted than Mario. He's quiet, shy, and doesn't like attention that much. He's more laidback and accepting than Mario is, but not nearly as confident. He also doesn't seem very confrontational, and probably prefers remaining in the background, unobtrusive. He doesn't like to confront people about things or how he feels and is far too shy or unsure of himself to speak his mind...

Or so I think.