King, 76, a former radio host from Brooklyn, is listed in the Guinness Book of World Records for having the longest running show with the same host in the same time slot on the same network.
King got his start as a radio host in 1957 in Miami Beach, where he'd frequently hobnob with the jet set of the day: Jackie Gleason, Bobby Darin and Lenny Bruce would all appear on a program he hosted from a restaurant called Pumpernick's, according to King biographer Peter Occhiogrosso.
"He led the life. He bet on the horses a lot, got into some gambling debts and things like that," Occhiogrosso told ABC News. "He liked the action and he liked not knowing what was going to happen."
King's interviewing style famously eschews any rigorous preparation. Occhiogrosso says King prefers knowing as little about his guest as his audiences do, using a frank and downhome approach that attracted guests who would otherwise not do television interviews.
Ever since debuting on the fledgling CNN in 1985, his show has been a cross-section of A-list political and entertainment celebrity interviews and conversations with crackpots and conspiracy theorists. On the week in which he celebrated his 25th anniversary, he spoke to basketball star LeBron James, Bill Gates, President Barack Obama and Lady Gaga.
King said he began thinking about stepping down as he flew home to Los Angeles from Akron, Ohio, where he interviewed James.
"I said, 'I can't top this,'" King recalled in an interview with The Associated Press Tuesday.
In 1993, when King paired Al Gore and Ross Perot for a debate about NAFTA, he set a cable news ratings record that still stands: 16.3 million viewers.
"He helped change the course of an election in 1992 with Ross Perot, getting him to announce his campaign on his show," says Haddad, his former producer. "He was the first talk show host on cable news who proved you could get an audience with interviews and talking about news."
King, who repeatedly remarked on Tuesday's show that he wanted to spend more time with his family, had also recently been having widely publicized difficulties with his seventh wife, Shawn Southwick.
King filed for divorce from Southwick, 50, April 14 in Los Angeles Superior Court, citing "irreconcilable differences" and asking for joint custody of their children.
But a week later the two were said to be back together and in counseling. In May 2010, Southwick overdosed on prescription pills.
Whatever the reason for his departure, King has said that if it were up to him, American Idol emcee Ryan Seacrest would be his choice to fill his shoes, according to The Associated Press. Earlier this month the New York Post reported that CBS anchorwoman Katie Couric, whose own contract is set to expire, is not interested in King's job. Also widely speculated as a potential replacement is Piers Morgan, the former tabloid newspaper editor and winner of Celebrity Apprentice.
Whoever ends up in King's chair, one thing is clear: he or she will have a mighty large pair of suspenders to fill.