Hello Kitty is one of the many fictional characters produced by Sanrio, a Japanese company that makes many cute characters, and is also one of the most well known ones. She is a white kitty with no mouth, hence her originally-proposed name being Kitty White.
Hello Kitty has appeared in a lot of animutations (the most of any female character), to the point where she is a recurring character. In JamezBond, she can be used as an effective source of renewable electrical energy. She has also been in battles, including ones in Fun With Pop Culture, where she beat Mr. T and Duck King, and one in We Drink Ritalin, where she lost against Dave Frishberg. And despite her usually having no mouth, she has had one in at least five animutations: Rock And Roll Mcdonalds, Shumway, Light Tight (Learning French Lesson 2), HALALSLl.swf, and Burgercat!
Hello Kitty article on Wikipedia.org