"I worked really hard through a very tumultuous time at the 'Today' show," Zucker said in a talk posted on YouTube this year by IMG Speakers.
"Under his leadership at 'Today,' the program was the nation's most-watched morning news show and the most profitable program on television," says Zucker's official biography on the GE website, from his days at NBC. "Zucker has also served as executive producer of NBC's coverage of several major events, including the 'Decision 2000' election night broadcast, the 1993 and 1997 presidential inaugurations and the Persian Gulf War."
In 2000, Zucker was named president of NBC Entertainment. He then rose through the ranks, becoming president of the network's Entertainment, News & Cable Group and, in 2005, CEO of the NBC Universal Television Group.
As NBC's ratings fell, many critics blamed Zucker, with some chalking it up to his record developing sitcoms.
Still, in 2007, Zucker was again promoted, becoming CEO of NBC Universal.
Zucker left NBC in 2010, after the company merged with Comcast.
He launched Katie Couric's talk show this fall. Entertainment Weekly reported in October that the program was among the new talk shows "leading" in the ratings, but The Hollywood Reporter said "Couric's middling ratings and topics" had "affiliates grumbling."
A Harvard graduate, Zucker showed an interest in journalism during his college years. He was editor of the Crimson, the school's daily newspaper.
O'Brien at the time ran the Lampoon, the school's humor magazine -- and Zucker once had O'Brien arrested over a prank.
"Zucker is one of the most competitive guys you'll ever meet," Fortune writer Patricia Sellers said in 2010.
Zucker will now bring that competitive instinct and willingness to take risks to CNN -- along with lessons learned.
"The challenge Zucker faces is boosting CNN's ratings during those long periods when there's no major breaking story, and creating a more clearly defined brand for the network," said Kurtz. "He certainly has the drive and experience to lead an overhaul as CNN tries to compete with its more ideological cable rivals."