It seemed ludicrous that the man credited with inventing Bitcoin - the world's most wildly successful digital currency, with transactions of nearly $500 million a day at its peak - would retreat to Los Angeles's San Bernardino foothills, hole up in the family home and leave his estimated $400 million of Bitcoin riches untouched. There are several Satoshi Nakamotos living in North America and beyond - both dead and alive - including a Ralph Lauren menswear designer in New York and another who died in Honolulu in 2008, according to the Social Security Index's Death Master File. There's even one on LinkedIn who claims to have started Bitcoin and is based in Japan. The eldest of three brothers who all work in engineering and technical fields, Nakamoto graduated from California State Polytechnic University in Pomona, Calif., with a degree in physics. Nakamoto's family describe him as extremely intelligent, moody and obsessively private, a man of few words who screens his phone calls, anonymizes his emails and, for most of his life, has been preoccupied with the two things for which Bitcoin has now become known: money and secrecy. For the past 40 years, Satoshi Nakamoto has not used his birth name in his daily life. At the age of 23, after graduating from California State Polytechnic University, he changed his name to "Dorian Prentice Satoshi Nakamoto," according to records filed with the U.S. District Court of Los Angeles in 1973. Since then, he has not used the name Satoshi but instead signs his name "Dorian S. Nakamoto." Descended from Samurai and the son of a Buddhist priest, Nakamoto was born in July 1949 in the city of Beppu, Japan, where he was brought up poor in the Buddhist tradition by his mother, Akiko. In 1959, after a divorce and remarriage, she immigrated to California, taking her three sons with her. Now age 93, she lives with Nakamoto in Temple City. Just after graduating college, Nakamoto went to work on defense and electronics communications for Hughes Aircraft in southern California. Nakamoto has six children. The first, a son from his first marriage in the 1980's, is Eric Nakamoto, an animation and 3-D graphics designer in Philadelphia. His next five children were with his second wife, Grace Mitchell, 56, who lives in Audubon, N.J., and says she met Nakamoto at a Unitarian church mixer in Cherry Hill, N.J., in the mid-1980s. She recalls he came to the East Coast after leaving Hughes Aircraft, now part of Raytheon, in his 20s and next worked for Radio Corporation of America in Camden, N.J., as a systems engineer. In 1987, the couple moved back to California, where Nakamoto worked as a computer engineer for communications and technologies companies in the Los Angeles area, including financial information service Quotron Systems Inc., sold in 1994 to Reuters, and Nortel Networks. Nakamoto, who was laid off twice in the 1990s, according to Mitchell, fell behind on mortgage payments and taxes and their home was foreclosed. That experience, says Nakamoto's oldest daughter, Ilene Mitchell, 26, may have informed her father's attitude toward banks and the government. Around 2000, Nakamoto and Grace separated, though they have never divorced. They moved back to New Jersey with their five children and Nakamoto worked as a software engineer for the Federal Aviation Administration in New Jersey in the wake of the September 11 attacks, doing security and communications work. When the FAA contract ended, Nakamoto moved back to Temple City, where for the rest of that decade things get hazy about what kind of work he undertook.