She is credited with changing the way people talk to each other, having popularized a confessional interview style that has coaxed secrets, revelations and often tears from guests of all kinds.

Winfrey, 55, who has struggled with her own weight issues while in the public spotlight, has also become a spiritual icon, urging viewers to find their true selves, follow their intuition and find inner peace and happiness.

"She blazed a trail," said Ellen Degeneres, a comedian who hosts her own daytime talk show, "Ellen."

"She will always be the queen of daytime."

Born into a life of poverty and abuse in Mississippi, Winfrey began her broadcasting career while she was still in high school and landed a job as a news anchor in Nashville at age 19.

Her emotional ad-libs won her a Chicago morning talk show in 1984, which beat rival Phil Donahue for the top spot locally within a month and was syndicated nationally in 1986.

Now broadcast in 145 countries, "The Oprah Winfrey Show" remains the top-rated talk show of all time and is estimated to reach 42 million U.S. viewers a week.

The show has served as the foundation for an empire that spans books, radio, magazines and the Internet and has launched the careers of a host of regular guests including counselor Dr Phil and chef Rachael Ray.

Winfrey began her own production company in 1988 and named it Harpo - her name backwards - and Forbes magazine declared her the first female African-American billionaire in 2003.

Winfrey is now estimated to be worth US$2.7 billion and is regularly ranked among the world's most powerful women, celebrities and media personalities.

"I certainly never could have imagined the yellow brick road of blessing that have led me to this moment with you," Winfrey told viewers Friday while announcing that she will take the show off the air in September 2011.

Fans won't have to look far for their Oprah fix: the Oprah Winfrey Network - OWN - is expected to be launched in January 2011.

Known as an almost uniquely influential tastemaker, Winfrey's recommendation of a book or product has an instantaneous and enormous effect.

Through her now-defunct televised book club she popularized works including Cormac McCarthy's "The Road."

Her stamp of approval was considered so important that she managed to convince the famously-reclusive author to appear on her show for his first ever television interview.

In 2008, she broke with a precedent of staying out of politics and endorsed fellow Chicagoan Barack Obama's presidential bid.

Her support was estimated by University of Maryland researchers to have brought in a million additional votes and helped Obama win both the Democratic nomination and the presidency.