As a top executive at Google for the past 13 years, Marissa Mayer played an instrumental role in developing many of the services that have tormented Yahoo as its appeal waned among web surfers, advertisers and investors.
Now, Yahoo is turning to its longtime nemesis to fix everything that has gone wrong while Google has been cementing its position as the internet's most powerful company.
Mayer, 37, will tackle the imposing challenge in taking over as Yahoo's fifth chief executive in the past five years.
Just a few hours after Yahoo ushered her in as its new chief executive, the struggling internet company's second-quarter earnings tempered some of the excitement surrounding her hiring.
The results provided a sobering reminder that Mayer is entering a situation dramatically different from what she left behind at Google, where she helped build the internet's dominant search and advertising service during her 13-year tenure.
Instead of pulling the levers on Google's finely tuned moneymaking machine, she will now be running a financial laggard seemingly unable to devise an effective turnaround strategy.
The surprise hiring announced this week indicates Yahoo still believes it can be an internet innovator instead of merely an online way station where people pass through to read a news story or watch a video clip before moving on to more compelling internet destinations.
"I just saw a huge opportunity to have a global impact on users and really help the company in terms of managing its portfolio, attracting great talent and really inspiring and delighting people," Mayer said.
Like her predecessors, Mayer will have to come up with an effective strategy to compete with the juggernaut that Google has become and the increasingly influential force that Facebook is turning into as more people immerse themselves in its social network.
Both Google, the internet's search leader, and Facebook have been beating Yahoo in the battle for web surfers' attention and advertisers' marketing budgets.
As Yahoo has lagged in that pivotal race, so has its financial performance and stock price.
The stock has been slumping since Yahoo balked at a chance to sell itself to Microsoft for US$47.5 billion ($59.6 billion), or US$33 per share, in 2008.
Yahoo shares haven't traded above US$20 since September 2008. The announcement came after the market closed on Tuesday. Yesterday, Yahoo shares slid US5c to close at US$15.60.
Yesterday Yahoo announced it had earned US$227 million for the three months ended in June. That was down 4 per cent from net income of US$237 million a year ago.
"If she can pull this off and turn around Yahoo, it will make her legacy," Gartner analyst Allen Weiner said of Mayer.
"Yahoo's iconic yodel has been missing for a long time. Her mission will be to bring that yodel back."
This will be the first time that Mayer has run a company as she steps out of the long shadow cast by the Google's ruling triumvirate co-founders Larry Page and Sergey Brin, along with executive chairman Eric Schmidt.
Although she had her responsibilities at Google narrowed two years ago, Mayer is still widely considered to be among the internet industry's brightest executives.
A Wisconsin native, Mayer is a mathematics whiz with a sponge-like memory and a keen eye for design.
Mayer joined Google in 1999 as its 20th employee and went on to play an integral role in helping Page and Brin exploit their online search technology to outmanoeuvre Yahoo at a time when it was still the larger of the two.
Now, it takes Google a little more than a month to generate as much revenue as Yahoo does in an entire year.
During Google's rise, Mayer helped oversee the development and design of the company's popular email, online mapping and news services.
She also became a topic of Silicon Valley gossip during Google's early years while she dated Page for three years. They have since got married to other people.
"We will miss her talents," Page, now Google's chief executive, said.
Schmidt hailed Mayer as "a great product person, very innovative and a real perfectionist who always wants the best for users. Yahoo has made a great choice".
Mayer becomes one of the most prominent women executives in Silicon Valley, a place whose geeky culture has been dominated by men for decades.
This is Yahoo's second female chief executive, though. Silicon Valley veteran Carol Bartz, 63, spent more than two-and-half years as Yahoo's chief executive before she was fired last September.
Within a few months, Mayer expects to be on a maternity leave. In another interview on Tuesday, Mayer revealed to Fortune magazine that she is pregnant with a boy.
Her due date is October 7. She said she had informed Yahoo's board about her pregnancy before the 11 directors unanimously voted to hire her.
Yahoo picked Mayer over an internal candidate, Ross Levinsohn, who had been widely considered to be the front-runner for the job after stepping in to fill a void created two months ago when the company dumped Scott Thompson as chief executive amid a flap over misinformation on his official biography.
Thompson's bio inaccurately said he had a college degree in computer science, an accomplishment that Mayer can rightfully list on her resume.
She earned a master's in computer science at Stanford University, the same school where the co-founders from both Google and Yahoo honed their engineering skills.
Mayer said she wasn't looking to leave Google when Yahoo first contacted her on June 18 about the job.
Her hiring threatens to alienate Levinsohn at a time when he has been steering Yahoo's recent emphasis on producing more original content and highlighting material provided by other media outlets in an effort to persuade its website's 700 million monthly visitors to stick around longer.
Recent partnerships include those with ABC News and the financial news channel CNBC.
"Marissa's first order of business should be convincing Levinsohn to stay," Gartner's Weiner said.
"If he leaves, there will be an exodus" among the Yahoo employees working on the content for the company's website.
Mayer declined to comment on any discussions she might have planned with Levinsohn.
Even if Levinsohn and his allies leave, Yahoo should still benefit from the connections and reputation that Mayer built during her years at Google, predicted JP Morgan analyst Doug Anmuth.
She will be greeted by at least one familiar face on Yahoo's senior management team. While serving as Yahoo's interim chief executive, Levinsohn last month lured away Google executive, Michael Barrett, to be Yahoo's chief revenue officer.
Mayer skipped Yahoo's conference call yesterday to discuss financial results with stock market analysts so she can start to get a better grasp on the task ahead of her.
She already has cancelled holiday plans for next month.
"For me work is fun, and fun is work," Mayer said.
"I am very excited about the big challenges here, and I can't wait to work on them. It's going to be very, very energising."
BRIGHT STAR
New Yahoo chief executive Marissa Mayer.
* Joined Google in 1999 as its 20th employee.
* Played an integral role in helping Google exploit its online search technology to outmanoeuvre Yahoo.
* Helped oversee the development and design of Google's popular email, online mapping and news services.
- AP