Roy Marcus Cohn (/koʊn/; February 20, 1927 – August 2, 1986) was an American attorney who became famous during Senator Joseph McCarthy's investigations into Communist activity in the United States during the Second Red Scare. Cohn gained special prominence during the Army–McCarthy hearings. He was also a member of the U.S. Department of Justice's prosecution team at the espionage trial of Julius and Ethel Rosenberg.
Born to an observant Jewish family in The Bronx, New York City, Cohn was the only child of Dora (née Marcus; 1892–1967) and Judge Albert C. Cohn (1885–1959), who was influential in Democratic Party politics. His great-uncle was Joshua Lionel Cowen, the founder and longtime owner of the Lionel Corporation, a manufacturer of toy trains. He lived in his parents' home until his mother's death, after which he lived in New York, the District of Columbia, and Greenwich, Connecticut.
After attending Horace Mann School and the Fieldston School, and completing studies at Columbia College in 1946, Cohn graduated from Columbia Law School at the age of 20. He had to wait until his 21st birthday to be admitted to the bar, and used his family connections to obtain a position in the office of United States Attorney Irving Saypol in Manhattan the day he was admitted.