Marlene Castro knew the tall blonde woman only as Laurene, her mentor. They met every few weeks in a rough Silicon Valley neighborhood the year that Ms. Castro was applying to college, and they e-mailed often, bonding over conversations about Ms. Castro's difficult childhood. Without Laurene's help, Ms. Castro said, she might not have become the first person in her family to graduate from college.

It was only later, when she was a freshman at University of California, Berkeley, that Ms. Castro read a news article and realized that Laurene was Silicon Valley royalty, the wife of Apple's co-founder, Steven P. Jobs.

"I just became 10 times more appreciative of her humility and how humble she was in working with us in East Palo Alto," Ms. Castro said.

The story, friends and colleagues say, is classic Laurene Powell Jobs. Famous because of her last name and fortune, she has always been private and publicity-averse. Her philanthropic work, especially on education causes like College Track, the college prep organization she helped found and through which she was Ms. Castro's mentor, has been her priority and focus.

Now, less than two years after Mr. Jobs's death, Ms. Powell Jobs is becoming somewhat less private. She has tiptoed into the public sphere, pushing her agenda in education as well as global conservation, nutrition and immigration policy.

"She's been mourning for a year," said Larry Brilliant, who is an old friend of Mr. Jobs. "Her life was about her family and Steve, but she is now emerging as a potent force on the world stage, and this is only the beginning."

But she is doing it her way.

"It's not about getting any public recognition for her giving, it's to help touch and transform individual lives," said Laura Andreessen, a philanthropist and lecturer on philanthropy at Stanford who has been close friends with Ms. Powell Jobs for two decades.

While some people said Ms. Powell Jobs should have started a foundation in Mr. Jobs's name after his death, she did not, nor has she increased her public giving.

Instead, she has redoubled her commitment to Emerson Collective, the organization she formed about a decade ago to make grants and investments in education initiatives and, more recently, other areas.

"In the broadest sense, we want to use our knowledge and our network and our relationships to try to effect the greatest amount of good," Ms. Powell Jobs said in one of a series of interviews with The New York Times.