LONDON — The former factory executive credited with resurrecting the Fiat and Chrysler brands — and then combining them — died Wednesday morning at the age of 66. Sergio Marchionne had abruptly resigned as CEO of Fiat Chrysler Automobiles on Saturday; the official announcement cited “unexpected complications” that arose in the days following his recovery from surgery for an undisclosed condition.

“Unfortunately, what we feared has come to pass. Sergio Marchionne, man and friend, is gone,” said John Elkann, a member of the Agnelli family, founders of the Fiat brand, in a statement. “Over the past 14 years together we have lived through successes and difficulties, internal and external crises, but also unique and unrepeatable moments, both personal and professional.”

Born in Chieti, Italy, in 1952, Marchionne emigrated with his family to Toronto, Ontario, Canada, at the age of 13. After earning an MBA from the University of Windsor and a law degree from York University, Marchionne worked as an accountant, tax specialist, and chief executive, first joining the automotive industry as Fiat S.p.A.’s CEO in 2004. Two years later, Fiat turned its first profit in five years; in 2009, Marchionne made the first of several moves that would result in the Italian’s carmaker’s acquisition of the struggling and recently bankrupt Chrysler Group and its rechristening as Fiat Chrysler Automobiles.

Marchionne was considered unique among industry executives — shrewd but genial and outspoken, favoring rumpled sweaters over jackets and ties, and committed to reviving the Fiat and Chrysler brands and merging the companies when the prevailing wisdom said it couldn’t be done.

“I believe that the best way to honor his memory is to build on the legacy he left us, continuing to develop the human values of responsibility and openness of which he was the most ardent champion,” Elkann said.

Michael Manley, an 18-year Chrysler veteran who most recently served as division head for FCA’s Ram and Jeep brands, was appointed to succeed Marchionne as FCA’s CEO.