The Andreessen Horowitz partner has the power to change your career—not just once, but repeatedly.

And as Business Insider found out from talking to Callahan, if you are a talented engineer, even one still in college, chances are she wants to meet you, too.

Callahan runs the talent network for Andreessen Horowitz, a venture-capital firm. Those who are in the talent network get first dibs at jobs at some of the Valley's hottest startups.

The network was a novel idea when it was started some 2.5 years ago, when Callahan joined Andreessen Horowitz, or A16z. (That's the geeky shorthand for the number of characters between "A" and "z".)

She knew cofounder Marc Andreessen because she lead HR at his previous company, Opsware, which HP bought for $1.6 billion in 2007.

Venture-capital firms have long played a matchmaking role between the startups they back and top talent. But they've typically focused on placing executives in top-level roles.

That focus on the C-suite ignored the chronic shortage of engineers and product managers in the Valley. Andreessen Horowitz believed that if you could find out a person's passions and match it with a startup working in that area, its startups would win the talent war.

But that meant getting to know thousands of Valley stars and college students.

The idea "actually works very well," Callahan reports.

"I wasn't sure that it would," she laughs.

But as a result of careful groundwork—not just casual interviews, but diligent research like scrutinizing engineers' code—the network is in full effect. A person in the network will call her team first when they start looking around, she says.