THE Oprah Winfrey Show is to end in September 2011 after more than two decades on air, the production company behind the programme has said. Billionaire Winfrey, 55, one of the most influential women in the US, has hosted the show since 1986. A spokesman for the stars Harpo production company would not say why Winfrey had decided to quit, but said she would discuss it on Fridays show. Winfrey is expected to focus instead on the launch of her own TV channel. She already runs a satellite radio station, Oprah Radio, with presenters including Dr Maya Angelou and therapist Dr Laura Berman. The sun will set on the Oprah show as its 25th season draws to a close on September 9, 2011, Tim Bennett, president of Winfreys Harpo production company, wrote in a letter to affiliates. The Oprah Winfrey Show, currently syndicated in 145 countries, has transformed the star into a cultural phenomenon. The shows open atmosphere and frank conversation redefined the talk show genre and made Winfrey the wealthiest black woman in the world. Her reputation was clearly appreciated by the big-name stars who opened their souls on her show, from Michael Jackson to Tom Cruise - who famously jumped on the sofa to announce his love for his future wife Katie Holmes. The introduction of Oprahs Book Club helped authors whose novels were selected become bestsellers overnight, and Winfreys support for US President Barack Obama was seen as crucial to his presidential election campaign. Winfreys empire also includes a magazine, books and, from 2011, a cable TV network. The Oprah Winfrey Network is a joint venture between Winfrey and Discovery Communications and is set to replace the Discovery Health Channel in more than 70 million US homes. Oprah is still the highest-rated US talk show with an average seven million daily viewers, but audiences are half what they were a decade ago. The end of the programme will be a blow to distributor CBS, which earns a percentage of licensing fees - estimated to be worth hundreds of millions of dollars - from the more than 200 local ABC TV stations across the US that broadcast it. BBC Many stations also built their schedules around Winfreys show, using it to promote other programmes while also delivering a large audience to their local news programming. BBC