On October 4, 1986, while walking along Park Avenue to his apartment in Manhattan, Dan Rather was attacked and punched from behind by a man who demanded to know "Kenneth, what is the frequency?" while a second assailant chased and beat him. As the assailant pummeled and kicked Rather, he kept repeating the question.

In describing the incident, Rather said “I got mugged. Who understands these things? I didn't and I don't now. I didn't make a lot of it at the time and I don't now. I wish I knew who did it and why, but I have no idea.” Until the crime was resolved years later, Rather's description of the bizarre crime led some to doubt the veracity of his account, although the doorman and building supervisor who came to Rather's aid fully confirmed his version of events.

The assault remained unsolved for some time, and was referenced multiple times in popular culture. The phrase "What's the frequency, Kenneth?" became a popular-culture reference over the years, such as in a scene in the graphic novel Like a Velvet Glove Cast in Iron by cartoonist Daniel Clowes.

The opening track of the 1987 album Lolita Nation by California power pop group Game Theory is titled "Kenneth, What's the Frequency?" In 1994, the band R.E.M. released the song "What's the Frequency, Kenneth?" on their album Monster. Rather later sang with R.E.M. during a sound check prior to a gig at New York's Madison Square Garden, which was shown the following night on the Late Show with David Letterman.

In 1997, a TV critic writing in the New York Daily News solved the mystery, publishing a photo of the alleged assailant, William Tager, who received a 12.5-to-25-year prison sentence for killing NBC stagehand Campbell Montgomery outside The Today Show studio in 1994. Rather confirmed the story: "There's no doubt in my mind that this is the person."

New York District Attorney Robert M. Morgenthau said "William Tager's identity as the man who attacked Mr. Rather was established in the course of an investigation by my office." Tager claimed he thought television networks were beaming signals into his brain. When he murdered the stagehand, Tager was trying to force his way into an NBC studio with a weapon, in order to find out the frequency the networks were using to attack him, so that he could block it. Tager was paroled in October 2010.