After serving in the U.S. Marine Corps from 1959 to 1963, the "Tommy Boy" actor headed off to play football at Columbia University in New York. After an impressive showing on the field, Dennehy decided that Columbia was not the school for him and transferred to rival Yale. It was there that he realized acting, not sports, was his true passion. —XFINITY Entertainment Staff (Photo by Stephen Lovekin/Getty Images)
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