William Henry Gates III made his best decision on October 28, 1955, the night he was born. He chose J.W. Maxwell as his great-grandfather. Maxwell founded Seattle's National City Bank in 1906. His son, James Willard Maxwell was also a banker and established a million-dollar trust fund for William (Bill) Henry Gates III.[1]

However:

Several writers claim that Maxwell set up a million-dollar trust fund for Gates. A 1993 biographer who interviewed both Gates and his parents (among other sources) found no evidence of this and dismissed it as one of the "fictions" surrounding Gates's fortune. Gates denied the trust fund story in a 1994 interview and indirectly in his 1995 book The Road Ahead.[2]

So I'm inclined to think it's not true, although it does seem a fairly wide-spread story.

But at the same time, Bill Gates did come from a rich family, so he wasn't going to starve if Microsoft didn't work out.

[1] http://philip.greenspun.com/bg/

[2] https://www.cs.mcgill.ca/~rwest/link-suggestion/wpcd_2008-09...