This is passage from Defrauding America by Rodney Stich: "Bowen said that he reported directly to William Casey in the CIA during the 1960s and 1970s. He indicated that Casey was with the CIA in a covert capacity after World War II and long before becoming its director in 1981."
"Casey was part of the OSS during World War II until it was disbanded by President Truman in 1947. He then became a covert operative for the CIA with no publicized connection to the Agency until 1981, when President Reagan appointed him Director of the CIA."