His fascination with cars was inspired by his father, Einar Petersen, a Danish-born truck mechanic who drove to desert towns in California to ply his trade with his son at his side.Using $400 in cash and credit from a friendly printer, he published the first 10,000 copies of Hot Rod in January 1948. In 1996, Forbes magazine estimated Mr. Petersen’s worth at $400 million. By then, he and his wife, the former Margie McNally, had already endowed the Petersen Automotive Museum; they married in 1963 and she is his only immediate survivor. Mr. Petersen, the chairman of Petersen Publishing, started Hot Rod in 1948 as a slick eight-page magazine that he sold for 25 cents, riding a motorcycle from racetrack to racetrack in Southern California. By 1996 — the year he sold the company for $450 million to a former president of Hearst Magazines, D. Claeys Bahrenburg, and the former general manager of the Hollywood trade paper Variety, Neal C. Vitale — the company had 27 regular monthly magazines and 30 others that were published sporadically, with a total circulation of about 43 million. Petersen Publishing went public in 1997, and in 2001, after several changes in ownership, it was sold to Primedia Inc.