"Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan, and everything in between. But he was one of a kind. He arrived in our lives as an alien — but he ended up touching every element of the human spirit. He made us laugh. He made us cry. He gave his immeasurable talent freely and generously to those who needed it most — from our troops stationed abroad to the marginalized on our own streets," President Barack Obama said in a statement. (AP)
Here's a look at some of many of Williams' tours with the United Service Organizations (USO).