Usama Fayyad’s colleagues say he battles monsters for a living. In the elite engineering circles that this former NASA rocket scientist inhabits, the job description passes for a wisecrack. However, like many jokes, there’s truth behind it. Fayyad is Yahoo’s chief data officer, possibly the first person to hold such a position. His role since he took the post in December 2004 has been to make both sense and money from the vast amounts of information Yahoo collects on the doings of 500 million people who visit its site every month.