William James O'Reilly Jr. was born on September 10, 1949, in New York City, and grew up to become one of the most recognizable and polarizing figures in American broadcast journalism. A conservative commentator, author, and television host, O'Reilly built a career spanning more than four decades, during which he established himself as a dominant force in cable news while also earning a reputation as a prolific writer of popular history.

O'Reilly's broadcasting career began during the late 1970s and 1980s, when he reported for local television stations across the United States before moving on to national roles at CBS News and ABC News. His reporting for CBS earned him two Emmy Awards and two National Headliner Awards for excellence in journalism. He went on to anchor the tabloid television program Inside Edition from 1989 to 1995, a role that raised his national profile considerably.

In 1996, O'Reilly joined the Fox News Channel and launched The O'Reilly Factor, a news commentary program that would define his career. The show became the highest-rated cable news program for sixteen consecutive years, and at the time of his departure, media analyst Howard Kurtz described him as "the biggest star in the 20-year history at Fox News." During his tenure, O'Reilly frequently appeared as a guest on The Daily Show with Jon Stewart, where his spirited debates with Jon Stewart became memorable television moments. In 2012, the two men faced off in a charity debate billed as "The Rumble in the Air-Conditioned Auditorium" at George Washington University. O'Reilly also conducted a notable interview with President Barack Obama before Super Bowl XLVIII in 2014.

Beyond television, O'Reilly co-authored a series of bestselling historical books with Martin Dugard, including Killing Lincoln, Killing Kennedy, Killing Jesus, and Killing Reagan, all of which appeared on The New York Times bestseller list. These works were adapted into television films for National Geographic, and two of the productions earned O'Reilly Primetime Emmy Award nominations. He also hosted The Radio Factor from 2002 to 2009, extending his reach into talk radio.

In 2017, O'Reilly was dismissed from Fox News following a report by The New York Times that he had settled five lawsuits involving sexual misconduct. Since leaving the network, he has hosted the No Spin News podcast, which expanded into a television program that aired first on Newsmax and later on The First. He continues to make frequent appearances on NewsNation, where he discusses political topics of the day. O'Reilly was previously married to Maureen McPhilmy, with whom he has two children.