Marianne Williamson made a splash on the stage at Tuesday night's Democratic debate. In one particularly talked-about moment, Williamson appeared to yodel, her voice cracking as she passionately discussed health care. Another instance saw her evoke "Seinfeld" as she dropped a "yada, yada, yada" while discussing gun control. So who is she? Williamson is a self-help guru and best-selling author most recognized for being Oprah Winfrey's spiritual adviser.