Errol Morris in the context of "The Thin Blue Line (1988 film)"

"There are unknown unknowns" is a phrase from a response United States Secretary of Defense Donald Rumsfeld gave to a question at a U.S. Department of Defense (DoD) news briefing on February 12, 2002, about the lack of evidence linking the government of Iraq with the supply of weapons of mass destruction to terrorist groups. Rumsfeld stated:

The statement became the subject of much commentary. In The Decision Book (2013), author Mikael Krogerus (de) refers to it as the "Rumsfeld matrix". The statement also features in a 2013 documentary film, The Unknown Known, directed by Errol Morris.

Roger Joseph Ebert (/ˈiːbərt/ EE-bərt; June 18, 1942 – April 4, 2013) was an American film critic, film historian, journalist, essayist, screenwriter and author. He wrote for the Chicago Sun-Times from 1967 until his death in 2013. Ebert was known for his intimate, Midwestern writing style and critical views informed by values of populism and humanism. Writing in a prose style intended to be entertaining and direct, he made sophisticated cinematic and analytical ideas more accessible to non-specialist audiences. Ebert endorsed foreign and independent films he believed would be appreciated by mainstream viewers, championing filmmakers like Werner Herzog, Errol Morris and Spike Lee, as well as Martin Scorsese, whose first published review he wrote. In 1975, Ebert became the first film critic to win the Pulitzer Prize for Criticism. Neil Steinberg of the Chicago Sun-Times said Ebert "was without question the nation's most prominent and influential film critic," and Kenneth Turan of the Los Angeles Times called him "the best-known film critic in America." Per The New York Times, "The force and grace of his opinions propelled film criticism into the mainstream of American culture. Not only did he advise moviegoers about what to see, but also how to think about what they saw."

Early in his career, Ebert co-wrote the Russ Meyer film Beyond the Valley of the Dolls (1970). Starting in 1975 and continuing for decades, Ebert and Chicago Tribune critic Gene Siskel helped popularize nationally televised film reviewing when they co-hosted the PBS show Sneak Previews, followed by several variously named At the Movies programs on commercial TV broadcast syndication. The two verbally sparred and traded humorous barbs while discussing films. They created and trademarked the phrase "two thumbs up," used when both gave the same film a positive review. After Siskel died from a brain tumor in 1999, Ebert continued hosting the show with various co-hosts and then, starting in 2000, with Richard Roeper. In 1996, Ebert began publishing essays on great films of the past; the first hundred were published as The Great Movies. He published two more volumes, and a fourth was published posthumously. In 1999, he founded the Overlooked Film Festival in Champaign, Illinois.