To understand why Tim Armstrong just convinced Verizon to spend $4.83 billion to buy Yahoo's main business, you have to go back to April 2007.
Mr. Armstrong, then running North America advertising for Google, drove Google’s purchase of display ad firm DoubleClick, launching the search giant into banner advertising. By every measure it was a transformative deal, and it’s loomed large in Mr. Armstrong’s mind in the years since, multiple past colleagues say.
