Ezra Klein, the blogger who founded The Washington Post’s popular Wonkblog, will start a new commentary and news site backed by Vox Media, the three-year-old proprietor of SB Nation, a network of sports blogs and sites, and the Verge, a technology, culture and science Web site.

Klein, 29, announced his departure from The Post last week after the newspaper decided not to go forward with his plans for a new site.

In an interview Sunday, Klein said his future site — as yet unnamed — will have a wider focus than Wonkblog, which specializes in policy news and analysis. His site, which will have its a preliminary launch sometime in the spring, will eventually incorporate cultural topics and sports, he said.

Klein, who is a columnist for Bloomberg News and a contributor to MSNBC, is among a handful of journalists who are making the leap from mainstream news organizations to new digital journalistic ventures that aim to capi­tal­ize on the founders’ “personal brand,” or star power.

Among others, blogger Andrew Sullivan took his popular Dish blog independent last year. New York Times statistics whiz Nate Silver took his FiveThirtyEight.com blog to a new venture backed by ESPN. And Walt Mossberg and Kara Swisher left the Wall Street Journal last month to form a technology-news site called Re/code, with funding from NBC.

The Post passed on backing Klein’s proposed operation, although Klein never presented his idea directly to Amazon.com founder Jeffrey P. Bezos, according to people familiar with the negotiations. Last fall, Bezos became owner of The Post.

There were also no direct discussions about the cost of the operation, according to those sources. The major sticking point, they said, was how much independence the newspaper was willing to give Klein.

Klein described his departure from The Post as amicable.

At Vox, which is based in Washington, Klein said his venture will join a suite of sites that include SBNation.com, Polygon, Curbed, Eater and Racked. The Verge, which covers technology and culture, was co-founded in 2011 by Joshua Topolsky, a former Washington Post columnist.