Competitive zeal of Ballmer key element in Yahoo chase

For now, it seems Ballmer has kept his passionate side in check in choosing to walk away from a deal over the weekend rather than raise the bid amount or launch a hostile takeover.

But some see Microsoft Corp.'s decision as simply one more step in the dance and expect Ballmer to reprise his pursuit later this year if Yahoo Inc. is unable to turn around its business.

If the CEO commandeers Microsoft's coffers for another run at Yahoo, he could face increased pressure to justify the move: Is he motivated by fear, or competitive zeal? Or is chasing Yahoo a product of rational calculation?

Ballmer has exhibited both tendencies in nearly 30 years at Microsoft.

A marketing guru in a company full of software programmers, Ballmer is known as an aggressive Microsoft partisan, who once allegedly screamed that he would "(expletive) kill Google."

He has strained his vocal cords exhorting Microsoft employees at sales meetings. A preposterous dance he did in front of one audience earned him the lasting nickname Monkey Boy. Video of it is widely available on the user-contribution site YouTube owned by Google Inc.

"I'm well known not to be the world's best negotiator," Ballmer told a tech conference this year after the Yahoo deal was first put on the table.

Yet behind his jovial presence and booming voice, Ballmer reveals a deep understanding of technology and a sharp mind. Ballmer is pragmatic and realistic even if animated. At Harvard University, where he met Bill Gates in the early 1970s, he beat Microsoft's founder on a national math test.

Rob Horwitz, chief executive of the independent research group Directions on Microsoft, landed a job at Microsoft in the mid-1980s after interviewing with Ballmer, whom Horwitz described as intense but likable, and blessed with an uncanny memory for people.