(Adds details on Cook's growing public presence, background)
March 26 (Reuters) - Apple Inc Chief Executive Tim Cook is joining the roster of the very rich who are giving away their wealth.
Fortune magazine cited the head of the world's largest technology corporation as saying he planned to donate his estimated $785 million fortune to charity - after paying for his 10-year-old nephew's college education.
"You want to be the pebble in the pond that creates the ripples for change," Cook told the magazine.
Fortune estimated Cook's net worth, based on his holdings of Apple stock, at about $120 million. He also holds restricted stock worth $665 million if it were to be fully vested.
The 54-year-old CEO's revelation in Fortune's lengthy profile of him is an example of the increasingly public philanthropy of the world's richest people.
Billionaire financier Warren Buffett is encouraging the very wealthy to give away at least half their worth in their lifetimes through the "Giving Pledge," whose website lists such luminaries as Microsoft Corp's Bill Gates, Mark Zuckerberg of Facebook Inc and Oracle Corp's Larry Ellison.
While Cook's largesse could not begin to approach the scale of a Gates or Zuckerberg, both worth billions of dollars, the Apple CEO told Fortune he hopes to make a difference.
Cook, who is not listed on the website, is known as an intensely private person who shuns the spotlight on philanthropy.
In recent years, however, he has begun speaking out more openly about issues ranging from the environment to civil rights. Cook, who recently revealed he was gay, spoke out against discrimination of the lesbian, gay, bisexual and transsexual communities during his induction into the Alabama Academy of Honor last year.
He told Fortune he has started donating money to unspecified causes quietly and is trying to develop a more "systematic approach" to philanthropy that goes beyond writing checks. (Reporting by Ankit Ajmera in Bengaluru and Edwin Chan in San Francisco; Editing by Sriraj Kalluvila and Andre Grenon)