Apple CEO Tim Cook is thinking big when it comes to giving back.

The head of the world's most valuable company is planning to give away his estimated $785 million fortune to charity — but only after paying for his 10-year-old nephew's college education, according to Fortune.

"You want to be the pebble in the pond that creates the ripple for change," Cook told the publication.

Based on his holdings of Apple stock, Fortune estimated Cook's net worth at about $120 million. He also holds restricted stock worth $665 million if it were to be fully vested.

Cook told the magazine he has already been "quietly" donating money to unspecified causes, but plans to adopt a "systematic approach to philanthropy" in the future that goes beyond simply writing checks. The CEO is passionate about issues such as stopping the transmission of AIDS, human rights, and immigration reform.

Known as an intensely private man, Cook has begun speaking more openly as of late about causes such as lesbian, gay, bisexual, and transgender protections. The Apple head honcho, who recently came out as gay, was inducted into the Alabama Academy of Honor late last year, and in his acceptance speech, he challenged his home state to do more to protect the rights of its LGBT community.

"We can't change the past," the CEO said, "but we can learn from it, and we can create a different future."

Meanwhile, besides giving away his fortune, there's another thing Tim Cook was willing to donate — his own liver. The new biography Becoming Steve Jobs claims that Cook offered an ailing Jobs a "portion of his own liver."

"After discovering that he shared a rare blood type with his sick colleague, and undergoing a battery of tests at a hospital 'far from the Bay Area, since he didn't want to be recognized,' Cook offered his liver to Jobs — only for Steve to turn it down," the biography relates.

Other tech CEOs have made similar philanthropy pledges, meanwhile, including Bill Gates and Mark Zuckerberg.