Yahoo is hiring longtime Google executive Marissa Mayer to be its next CEO, the fifth in five years as the company struggles to rebound from financial malaise and internal turmoil. Mayer, who starts at Yahoo Inc. on Tuesday, was one of Google's earliest employees and was most recently responsible for its mapping, local and location services. Mayer, 37, began her career at Google in 1999 after getting her master's degree at Stanford, the school Google's co-founders attended.