American-born heiress Blair Parry-Okeden, who lives at Scone in NSW's Hunter Valley, has topped Forbes Australia's rich list.
She ended the West Australian mining magnate Gina Rinehart's five-year run as the magazine's richest Australian. 
Forbes put Ms Parry-Okeden's net worth at $12.5 billion.
Ms Rinehart's fortune fell $4.54 billion to $12.1 billion courtesy of falling iron ore prices and a legal fight with her children that affected her shareholding in Hancock Prospecting.
Ms Parry-Okedon, 65, inherited a 25 per cent stake in the family's media empire, Cox Enterprises, after her mother's death in Hawaii in 2007. Her grandfather was a three-time governor of Ohio, and she married into this country's landed gentry.
She remains the lowest profiled of the Australian rich and has never spoken to the media.
She trained as a teacher after graduating from the La Pietra - Hawaii School for Girls, which her mother had helped found.
She came to Australia from Hawaii in the late 1970s after marrying into remnants of the NSW squattocracy, Simon Parry-Okeden, the son of prominent agriculturalist William Nugent Parry-Okeden, a former executive director of the Royal Agricultural Society of NSW. The couple, now divorced, raised two sons, Andrew, 35, and Henry, 33, both living in Australia.
Her most public outing was in 1989 when a children's book, Down by the Gate, was published. It tells the story of Australian native animals applying for a job on a farm after Mother Goose had placed an advertisement in a newspaper.
Ms Parry-Okedon lives at Rockview Station in Scone and has no role at the media company, America's third-biggest cable TV company. Forbes ranked Ms Parry-Okeden as the 16th richest woman in the world.
Her grandfather, James M. Cox, founded Cox Enterprises in Dayton, Ohio after purchasing the Dayton Daily News in 1898. Her grandfather even ran for the presidency of the United States in 1920, as the Democratic candidate.
Forbes also reported Ms Parry-Okedon had taken out Australian citizenship. She reportedly owns a cottage at Burradoo in the NSW Southern Highlands and a bolthole in Mosman and is a benefactor of Sydney Church of England Grammar School (Shore).
She is known as a reclusive philanthropist. Among her other donations, she gave $2 million to the University of Hawaii to endow a professorship at the university's Centre on Ageing
Ms Rinehart's fellow WA iron ore miner Andrew Forrest's wealth took the biggest percentage hit: down 41 per cent, sending him down 12 spots on the rich list to No. 22.
Top 10 richest Australians:
1) Blair Parry-Okeden, $12.5 billion
2) Gina Rinehart, $12.1b
3) Harry Triguboff, $9.9b
4) Frank Lowy, $7.1b
5) Anthony Pratt, $5.1b
6) James Packer, $4.9b
7) John Gandel, $4.5b
8) Lindsay Fox, $4b
9) David Teoh, $2.76b
10) David Hains, $2.7b