evil twin [ee-vuhl-twin]
1. A doppelganger, a copy, a counterpart, a clone, a reproduction, a duplicate, and/or something/someone similar to the original, but in other many ways the opposite in character, function, actions, etc.
EX. Evil twins; Superman has Bizarro, Mr. Spock has Mirror-Spock, and last, but not least is our subject of the day, Mario had Wario. In 1992, in Super Mario World 2: Six Golden Coins, the team working on the title were not exactly pleased to be working on a Mario game instead of making their own original title/characters and, rather than make a bad game or just be grumps about it, they created Wario as a symbol of their displeasure. His name was literally a combination of Mario and "warui" (悪い), literally translated as "bad". The character was used as the antagonist in the title, taking over Peach's Kingdom while Mario was busy in the events of Super Mario World, before Mario returned and kicked his butt out. The weird thing is...Wario isn't technically a villain.
In fact, despite his greedy, gluttonous, selfish, rude, crude, and seemingly jerkish attitude, Wario is an anti-hero that often rises to the situation (especially if it in his favor to do so). He has aided Mario on a few occasions, saved his own home land from invaders, and known to show some generosity when prompted. In the Wario Land series, he is usually the far lesser of two evils, a bit greedy but also willing to save the weak, and in the Warioware series (a persona favorite of mine) he wants to make his own videogames. The best example of his heroism in Super Mario 64, Wario helps Mario defeat Bowser as one of the additional playable characters.
In the end, Wario is so uncool, but that's okay. Every group of friends needs someone who is a little less than goody-goody and a little more contemptible.