Performance Art is related to the Happening, and is essentially the use of performance along with visual art. The roots of Performance Art can be seen in the "sound poems" that sprung from the Dada movement in the early 20th century. Indeed, most cultures have a precedent for Performance Art, though it hadn't been clearly defined within the art world until approximately 1970. Performance Art is now classified as having a few distinct properties. Performance Art is live, and while it may contain song, dance, or speech, it is not theater. Other than these basic guidelines, Performance Art is incredibly diverse. Yves Klein, a Performance Art trailblazer, completed several works that embodied the spirit of the genre. In The Void, Klein managed to create tremendous anticipation for his exhibition at the Iris Clert Gallery, drawing thousands of people to the venue. Upon entering, it was found that Klein had emptied the gallery but for a single cabinet, and painted everything white. The influences and themes of Performance Art are seemingly limitless, and overlaps with other styles such as Body Art and Fluxus occur. Ritual and sadomasochism have been the subjects of many artists, such as Vito Acconci, and the virtual patron saint of Performance Art, Joseph Beuys. Other strains of Performance Art include the rock concerts of musician Laurie Anderson, the videos of Bruce Nauman, and the “living” sculptural self-portraits of Gilbert and George.