Max Levchin on Yahoo CEO Marissa Mayer: 'Hardest working CEO in Silicon Valley bar none'

There's a lot of hard-working CEOs in Silicon Valley, but former Yahoo director Max Levchin believes no one tops Yahoo boss Marissa Mayer.

Despite recently giving up his seat on Yahoo's board, Levchin reiterated his support for Mayer during an interview with Bloomberg West's Emily Chang on Wednesday, noting that his confidence in the embattled CEO remains "certainly high."

"She is the hardest working CEO in Silicon Valley, bar none," Levchin said. "I think she deserves a tremendous amount of credit for that."

Levchin's defense of Mayer comes against a growing chorus of detractors, who fault Mayer for failing to revitalize Yahoo's business in her more than three years at the helm. Just yesterday, activist shareholder Starboard sent a letter to Yahoo's board, urging a management change.

Without getting into the specifics, Levchin pointed out that Mayer's hard work is most reflected in Yahoo's "genuine successes," from product development and the shift to mobile, and some of the new revenue streams created under her watch.

"There's an enormous amount of legacy challenges the company has to contend with and they're very real and they'll take a while," he continued. "But I doubt there's anybody out there better qualified to do it [than Mayer]."

Google allies

Levchin has long had a friendly relationship with Mayer. He worked with her at Google when his media-sharing startup Slide was acquired by the company in 2010, and was the first new board member to join Yahoo after Mayer was named CEO. Levchin recently stepped down from Yahoo's board citing commitments to his current startup, Affirm.

But Levchin isn't the only person to praise Mayer's crazy work ethic. Her long hours at Google are near-legendary, as one former Google exec once told us, "she will literally work 24 hours a day, 7 days a week." Salesforce CEO Marc Benioff recently called her, "completely magical."

Even last month, Mayer pulled through one of the most challenging periods of her time at Yahoo, running 3-day meetings and addressing the media - right until the day before she gave birth to twin babies.

But despite all the hard work, her time at Yahoo has drawn mixed results. Yahoo's growth has been slowing down and investors are increasingly growing impatient with her performance, giving nearly zero value to Yahoo's core business.

According to Business Insider's Biz Carson, Yahoo is preparing to cut 10% or more of its workforce this month, as the company preps for a major organizational shake up.

Mayer, for her part, has defended her performance in a recent CNBC interview, underscoring how Yahoo has overhauled its legacy business and created new revenue streams under her management.

"In 2012, when I joined Yahoo, all of our revenue streams were in decline," she said during the interview. "Today, we have futuristic monetization opportunities, and revenue that is growing as much as 50% year-over-year in terms of mobile, video, native, and social."

But Mayer's time at Yahoo may be limited. Starboard indicated in its letter Wednesday that it would run a proxy fight if Yahoo doesn't change its management, board members, and strategy.

"We think it is inevitable that the company undergoes significant change in the next 6 months," SunTrust's analyst Robert Peck wrote in a note yesterday.