Italian automotive executive and grandson of Giovanni Agnelli (Agnelli, Giovanni), the founder of Fiat SpA. He served as the company's chairman from 2003 to 2004.

After graduating from the University of Turin with a law degree in 1959, Agnelli joined the family's automotive enterprise, Fiat. He assumed the presidency of Fiat France in 1965 and in five years doubled sales in that country. When he was made president of Fiat International, he increased Fiat sales and made the car the most popular in western Europe and doubled its sales in the United States. These successes pulled Umberto out of the shadow of his brother Giovanni (Agnelli, Giovanni), 13 years his senior and the president of the parent firm.

After becoming Fiat's managing director, Agnelli instituted progressive reforms for company workers. He offered flextime, which allowed workers to choose their own hours within limits. He became vice-chairman of Fiat SpA in 1976 and president of Fiat Auto in 1980, resigning his post as managing director of the parent company. From 1976 to 1979 he also served as a senator in Italy. Following Giovanni's death in 2003, Agnelli became chairman of Fiat SpA. At the time, the company was in sharp decline, and Agnelli oversaw a number of measures that improved its financial situation.