Photo: Asa Mathat

New Yahoo (YHOO) chief executive Marissa Mayer is the youngest CEO of a Fortune 500 company. At 37, she displaces her former boss, 39-year-old Google (GOOG) CEO Larry Page.

Mayer is also the youngest woman ever to make the Fortune Most Powerful Women list. In 2008, at 33, she locked down the No. 50 spot -- and rose to No. 38 on the 2011 MPW list.

Though Mayer has famously described herself (again and again) as a geek, she's no stranger to the spotlight. Her charisma, as well as that infectious laugh, grabbed the attention of the masses and helped her become one of Silicon Valley's most visible faces. Digging through Fortune's trove of Marissa Mayer articles, we've compiled a timeline that captures the brains, energy, and quirks of Yahoo's new CEO.

How I work: In 2006, Google's then VP of Search Products and User Experience told Fortune, "I don't feel overwhelmed with information. I really like it." In an average week, Mayer claimed she has about 70 meetings scheduled, taking up 10 or 11 hours a day. In hopes of making unproductive time productive, she uses wait time to make personal calls to catch up with family and friends. "I pace myself by taking a week-long vacation every four months," she added.

Marissa Mayer: On the hot seat: A year later, Fortune sat in on one of Mayer's design meetings. When the first team presented several design revisions that looked like a "slam dunk," according to the writer, Mayer remained unimpressed. "It looks pretty noisy if you look at the base data," she told the duo, asking if the searches/per user/per day graph was available. "Uh, no," they replied. "Well, that's a good macro statistic that indicates user happiness. So can we see that one too?" she asked. The numbers, according to Mayer, are where the answers reside.

New Valley Girls: In 2008, the year Mayer first made the MPW list, she told writer Pattie Sellers a story about helping a female employee understand how to behave in a male-dominated tech workplace. After the woman pushed her own idea by playing up how passionate she was about it, Mayer called her that evening. "She went emotional... I told her, 'If you were a guy, I probably would have waited until Monday morning to tell you. But you can't behave that way.'"

My tech "a-ha" moment: In 2008, Mayer talked with Fortune about her most radical career shift. "I started off at Google as a software engineer and was really comfortable (and really liked) programming. Shifting toward management meant greater responsibility and influence, but it also meant giving up programming day-to-day in my role, which was hard because it took me out of my comfort zone."

Marissa Mayer chats with former Yahoo! CEO Carol Bartz at the FORTUNE Most Powerful Women Silicon Valley dinner in 2010.

Google's top girl geek: At the 2010 Matrix Awards, an annual lunch honoring women in communications, Mayer told the crowd "I am a geek. I love to code." She uses spreadsheets to organize all aspects of her life, from cooking to planning her wedding. "Geeks are people who love something so much that all the details matter."

Marissa Mayer gets new gig (at Google): At the September 2010 Disrupt conference, an audience member asked Mayer, "I know you're happy at Google but let's assume you quit tonight and you leave what would you be interested in building, like, what industry, what would you do?" Her response: "I really love building consumer web products... Organizing information is a big passion of mine... Search is really interesting but I think there's also a lot of really interesting applications and I also think that in particular the mobile space, the location base space is something that's really exciting right now."

Google's Marissa Mayer on her dinner for the President: One week into her new role as VP of Location and Local Services at Google, Mayer held a political fundraiser at her Silicon Valley home for President Obama. The October 2010 chatter among the 60 guests (at about $30,000 a head) was about "innovation and jobs, along with the upcoming election," she said.

Google goes Gaga: Mayer interviewed Lady Gaga at Google in 2011.

Marissa Mayer and Susan Mashibe on Charlie Rose: Mayer, an annual participant in the Fortune/State Department Global Women's Mentoring Program, appeared on Charlie Rose with her mentee, Tanzanian entrepreneur Susan Mashibe in May 2011. Mayer hosted Mashibe at Google (and in her Silicon Valley home) for a month -- and asked Mashibe to assist she and her team with building Tanzania out on Google Maps.

Google VP Marissa Mayer's mobile challenge: At Fortune Brainstorm Tech in Aspen in July 2011, Fortune editor at large Pattie Sellers spotted a pedometer on Mayer's wrist. The Google VP said she had created a "100 Mile  Month Challenge" at Google. Mayer later held the closing ceremonies in her backyard, claiming to the crowd of 200-plus Googlers and friends, "We walked more than once around the earth at the equator—or 16.7 times around the moon."

I thought Google had a 2% chance of success: Mayer told the audience at the 2011 Fortune Most Powerful Women Summit, "It's totally fine to fail, you just have to fail fast." That is, don't invest huge time and resources into any idea until it's been proven successful.

Google's Marissa Mayer: How I got ahead: As the main speaker at the 2011 Fortune Most Powerful Women dinner in Palo Alto, Mayer shared three simple tips on getting to the top: Show up, surround yourself with the smartest people, and do something you're not quite ready to do.

Wal-Mart recruits a Googler, and it's a trend: In April 2012, Mayer was recruited by Wal-Mart (WMT) to join its board of directors.

New Yahoo CEO Mayer is pregnant: On July 16, Mayer was named Yahoo's new CEO. That evening, Mayer told Fortune exclusively that she's expecting a baby boy, due October 7. Will she be able to make Yahoo innovative and great again? That's the biggest question. Meanwhile, Mayer's step up to a high-profile CEO job while pregnant has inspired businesswomen around the world. She is an embodiment of Sheryl Sandberg's "Don't Leave Before You Leave."

With thousands of employees -- and millions of a young women -- looking to her for inspiration, Mayer has been placed on a pedestal that leaves plenty of room for a fall. Yet looking at her history of impressive multitasking, Mayer will likely bask in the pressure.