Banksy is the most widely known graffiti artist in the world and has inspired many others with his stencil technique. Many of his pieces make political statements while others are just downright funny. In addition to checking out his own site, I'd recommend seeking out some of the news articles about his work. Some pretty wild stuff.
Although the picture shown is not as recognizable as some of his other work, it is one of my favorites.
And though his own site doesn't show all of his work, other examples can be found elsewhere online. A must click! LINK
