Larry Hillblom, multimillionaire founder of the DHL worldwide delivery company, died when his vintage seaplane plunged into the Pacific last May.
His simple will left $300,000 each to his two brothers and the rest, valued conservatively at $500 million, was to establish a trust to support medical research.
Mr Hillblom, a graduate of the University of California at Berkeley, instructed the trustees to "show particular attention to and benefit the research programmes conducted by the university".
The university is having to grapple with a complex legal problem before it can benefit from this gigantic windfall. Mr Hillblom moved from California to the Pacific island of Saipan in 1981, where he wrote his will a year later. He fished and golfed but, more strikingly, he is alleged to have fathered a series of children on several Pacific islands by teenage girls.
There are at least four paternity claims now filed against the estate, including one on behalf of an 11-year-old in the Philippines called Junior Larry Hillblom.
The university has sought to pass a new law in the Commonwealth of the Northern Marianas Islands, which includes Saipan, striking down claims of unacknowledged offspring. But it will take DNA testing - and likely years of litigation - to settle the issue, attorneys for both sides believe.