President Barack Obama and Secretary of Defense Chuck Hagel paid tribute to actor and comedian Robin Williams Monday. Williams, 63, was found dead in his northern California home Monday and officials said it appeared to be a suicide. Obama said in a statement issued Monday night that Williams "arrived in our lives as an alien — but he ended up touching every element of the human spirit," referring to Williams' late 1970s role in the TV show "Mork and Mindy." The president was on vacation on Martha's Vineyard, Massachusetts.