When Karl Rove worked for President Bush, he had so much influence that some called him "Bush's Brain." Valerie Jarrett is the woman known as the other side of Barack Obama's brain. Jarrett, a 51-year-old business leader and single mother, just may be the most powerful woman in Chicago besides Oprah. And she's earned the complete confidence of Barack and Michelle Obama.

Jarrett talks about her 17 years with the Obamas and...