If you have an application open, Alt+F4 will shut it down. If you do not have an application running, it will shut down the computer.
Lemon Demon aka Neil Cicierega.The video was animated by AltF4 aka Shawn Vulliez.
"The Ultimate Showdown" was posted to the AlbinoBlackSheep website on January 6th of 2006 by Canadian animator Shawn Vulliez, under the alias "AltF4".