When Oprah bestows her approval, brands generally benefit. This may be as true in politics as it is in publishing. Winfrey's endorsement of Barack Obama in May 2007 was the first she had ever made for a Presidential candidate, and it sparked a surge of support for the Illinois Senator. Economists at the University of Maryland calculated that the Queen of Talk's public support was responsible for more than 1 million votes in the Democratic primaries, while the New York Times editorial board claimed that "a good chunk of credit" for Obama's victory in the general election should be attributed to Oprah.
Top 10 Oprah Moments
In honor of Oprah's birthday, TIME looks back at the talk-show host's most memorable moments, from her interview with a love-struck Tom Cruise to an unforgettable car giveaway