15 Most Frequent Celebrity Guests

13 (tie). Maria Shriver

Just like her late parents Sargent Shriver and Eunice Kennedy Shriver, Maria Shriver is changing the world, one person at a time. Oprah and Maria, both former journalists, have been friends for decades, and this connection was evident during Maria's 16 appearances.

Over the years, Maria has shared her wisdom and grace with the audience, and spoken out about important topics like Alzheimer's disease and the September 11 terrorist attacks. She has also empowered young people to be their best selves. "To kind of become your own person was, and is continuing to be, a challenge. I see that even for my own kids, and I think every kid is entitled to be who they are," Maria said in April 2008.