Jerry Yang knew only one English word when he emigrated to the US from his native Taiwan 36 years ago: shoe.

He will today be more familiar with the word than ever, having to fill one of the largest - and recently emptied - pairs in Silicon Valley: those of Yahoo! chief executive Terry Semel.

Mr Yang, one of Yahoo!'s co-founders, was the obvious choice to take over from Mr Semel, analysts said, having been at the company throughout its 13-year life and being intimately familiar with the areas of strategy and business development, where he has spent time most recently.

Although several suggested that in the long term, Sue Decker - until recently Yahoo!'s chief financial officer - may take over, Mr Yang was a safe pair of hands to ease the market's concerns in the short term, being a "known commodity" in the market with a vision for how to remake the company since it lost its market lead to Google.

Mr Yang, 38, was studying for a PhD in electrical engeneering at Stanford University when he and a fellow student, David Filo, created a directory of websites, in 1994.

The service was originally called 'Jerry and David's Guide to the World Wide Web', but was renamed Yahoo the following year because, the founders said, they liked the definition of yahoo - "rude, unsophisticated, uncouth".

(According to another snippet of Silicon Valley folklore, Yahoo! was in fact an acronym for "Yet Another Hierarchical Officious Oracle.")

When the pair realised the business potential of their idea, they postponed their doctorates indefinitely and founded the company, which went on to become one of the most popular online portals, netting Mr Yang an estimated $2.2 billion, according to Forbes.com.

Mr Yang choked up yesterday when he spoke about his time at Yahoo! under Mr Semel, who took over the running of the company in 2001. "It is an emotional time for us," he said. Mr Semel has been "a true role model and a mentor to me", adding that his boss had helped him "learn how to become a better leader and a better person".

He maintained, however, that he was well-equipped to lead the company through the challenges ahead: "I know the business and market dynamics well," he said. "Yahoo is in the midst of a multi-year transformation…It's imperative that we execute with speed and clarity and discipline."

Mr Yang was brought to California from Taipei at the age of two by his mother, a teacher, when his father died.

Despite knowing little English when he arrived, Mr Yang attended a local school, and went on to get bachelors and masters degrees from Stanford University, where he met his wife, Akiko Yamazaki, a wildlife conservation director.

Mr Yang has been intimately involved in Yahoo!'s strategy since founding the company, and is involved in every executive decision as well as being highly thought of by employees, according to insiders.

Until yesterday his title was "Chief Yahoo!", and he was described by Mr Semel during a conference call as "the heart and soul of Yahoo!".

"You couldn't get an outsider to understand the company better than Yang," said one executive, who spoke on the condition of anonymity to CNET news. "He's been the voice of the user for a long time."

Since late last month, Mr Yang has also had responsibility for the technology group following the resignation of the firm's technology officer, Farzad Nazem.

In his profile on the firm's website, Mr Yang is said to be "on a leave of absence" from his electrical engineering PhD.

It is unlikely he will be returning any time soon.