“He was tougher, smarter, smoother, and could be crueler than anybody I ever knew,” says Carl Colby of his father, CIA director William Colby, in a voice-over for his documentary The Man Nobody Knew. “I’m not sure he ever loved anyone, and I never heard him say anything heartfelt.” It’s a remarkably cold assessment of a father by his son, but one suspects that Bill Colby would have accepted it without blinking. A professional spy for nearly 30 years, Colby preferred reality to romance, hard intelligence to hopeful illusion. He also knew how to keep a secret; the bitter irony of his life is that, in the end, his most closely guarded secret turned out to be himself.

The Man Nobody Knew, which opens Friday for a weeklong run at Gene Siskel Film Center, operates on two parallel tracks, examining the personal and professional lives that Colby took great pains to compartmentalize. These two stories are what make the movie so fascinating, because they reveal two distinct, and largely conflicting, agendas. Carl Colby sets out to exonerate his father for the notorious Phoenix Program he masterminded during the Vietnam War (it was vilified on the left) as well as for his candid testimony to Congress as director of central intelligence in the 70s (he was vilified on the right). At the same time, Carl mounts a slow, steady, but ultimately withering attack on his father for the way he treated his family. The man revealed at the end of all this is a genuinely tragic figure who may have been betrayed by his country but can also be seen as having betrayed his wife and children.

As portrayed in the film, Colby could pass for the protagonist of a Graham Greene novel. He was a devout Roman Catholic and a liberal Democrat, but also a man of action; during World War II he served in the Office of Strategic Services as a special ops soldier, parachuting behind enemy lines in France and Norway. After graduating from Princeton University and earning a law degree from Columbia University, he joined the newly formed Central Intelligence Agency and spent many years in Rome, posing as a State Department officer as he clandestinely worked to undermine communist elements in the Italian political system. Interviewed for the film, his first wife, Barbara, warmly remembers their days in Rome, which gave them the opportunity to raise their children at the epicenter of the Catholic Church. But for Colby the church was also a powerful political instrument whose deep roots in the countryside made it a valuable source of intelligence.

Colby’s career is particularly worthwhile as a lens for viewing the Vietnam War, and the steady disintegration of the American effort in Southeast Asia pushed him to the limits of his personal morality. Stationed in Saigon from 1959 to ’62, he quickly realized that the security vacuum in the Vietnamese countryside was a dire threat to the presidency of Ngo Dinh Diem, and he helped administer the ill-conceived Strategic Hamlet Program, which attempted to protect peasants from communist insurgents by relocating them to fortified villages. Colby had returned to Washington to serve as deputy chief of the CIA’s Far East Division by the time of the coup against Diem, and the movie includes audiotape of him advising President Kennedy that the forces for and against Diem were evenly matched. The Colbys had been friendly with the Diem family, and as Barbara Colby recalls, her husband told her during Mass on All Saints’ Day that Diem had been killed.

Given the muted reaction last month to the CIA assassination of Anwar al-Awlaki, an American-born Islamist cleric living in Yemen, we may have a hard time grasping the controversy that erupted back in 1969 when the public learned about the Phoenix Program in Vietnam. By the time Colby had returned to Vietnam in 1968—leaving his wife and children behind this time—the Tet Offensive had turned the tide of American opinion against the war, and Colby took on the unenviable task of overseeing the new counterinsurgency program. Villagers loyal to the Vietcong were killed, imprisoned, and allegedly, in some cases, tortured to death; more than 26,000 people died at the hands of the Provincial Reconnaisance Units, many of whom were former Vietcong and some of whom were pursuing their own agendas. The brutality of their operations is evident from the movie’s archival footage: a headless corpse is dragged across the grass, and soldiers jam ace-of-spades playing cards into the mouths of the dead.

As Carl Colby recalls in voice-over, he and his siblings heard antiwar protesters compare their father to Heinrich Himmler. Yet various witnesses come forward in the film to defend Colby. “This was a guy who understood the hardness of life, and war, and what needed to be done against an enemy,” recalls Steve Young, a veteran of the program. When he questioned Colby about the ruthlessness of the PRUs, Colby replied, “Steve, the Indians are coming in through the windows. And you’ve gotta shoot back.” Robert McFarlane, who completed two tours of duty in Vietnam (and later, as national security adviser to President Reagan, became a key figure in the Iran-Contra scandal), explains, “It came down to making life better in a given village so that you engendered trust and ultimately gained intelligence from a much more welcoming community. At the same time, when you found somebody that the villagers identified as a bad guy, kill him. Quick.”

Colby’s career in the field may have been defined by the Vietnam War, but his career at home would ultimately be defined by the Watergate scandal. President Nixon brought him back from Vietnam in 1971 to become executive director of the CIA, and in April 1973, when the scandal forced Nixon to cut loose key advisers and reshuffle his administration, Colby was named director of central intelligence. Like the Phoenix Program, the directorship at that point was a dubious honor. No sooner had Colby taken on the job than the CIA inspector general delivered a report, commissioned by Colby’s predecessor, on some of the agency’s dodgy activities: plotting to assassinate Fidel Castro, spying on U.S. citizens, harassing antiwar activists, tapping the phones of journalists, conducting LSD experiments on human guinea pigs, consorting with organized crime figures. Colby was shocked by the 693-page report, whose revelations were soon tagged “the Family Jewels” and had the potential to destroy the CIA.

This crisis constitutes the film’s last chapter, and what makes it so fascinating is how completely Colby seems to have defied his own nature: secrecy had been his watchword for 25 years, yet he sized up the situation and concluded that only reform and a show of openness would save the agency. Seymour Hersh, the legendary investigative journalist, recalls in the film how Colby cooperated with him in the New York Times story that broke the news of domestic spying in December 1974: “He did not back away from the question of wrongdoing, and so that’s one hell of a story.” It set off a firestorm in Washington, and the Congress, emboldened by Nixon’s resignation four months earlier, launched a series of public hearings about the abuses of the CIA. Over the course of 1975—the “Year of Intelligence,” as it came to be known—Colby would be called to Capitol Hill on 32 separate occasions, and his frank testimony would eventually turn the Ford administration against him.

Carl Colby manages to score face time with several of the president’s men, each with his own ideas about what Bill Colby did. James Schlesinger, who preceded Colby as CIA director, thinks he was guilt-ridden over the recent death of his daughter Catherine, who had struggled with epilepsy, anorexia, and a depression stoked by her father’s role in Vietnam. Donald Rumsfeld, then President Ford’s chief of staff, thinks that Colby, as an intelligence professional, lacked the social and political skills to navigate the turbulent waters of Washington. But there’s no testimony from Ford’s secretary of state, Henry Kissinger, or secretary of defense, Dick Cheney, both of whom preferred that Colby keep his mouth shut. By January 1976 Colby had become damaged goods, and Ford replaced him with George H.W. Bush. News footage shows Colby, ever the good soldier, affably telling reporters he agrees with Ford’s decision.

The Colby family has never been forthcoming with memories of their famous patriarch. They declined to speak to John Prados, whose Lost Crusader: The Secret Wars of CIA Director William Colby is the only biography of Colby to date, and of his children, only Carl goes on the record here. But Barbara Colby does open up about her late husband, and her perspective adds a painful human dimension to the story. She recalls how she first learned that he’d joined the CIA: some neighbors in Washington reported to her that after dropping Bill off at his ostensible workplace, they’d seen him heading somewhere else. Being married to a spy could be lonely and disorienting: once, when they were in Italy, they ran into a couple they knew but when Barbara went to greet them Bill hushed her and they kept walking. “There were times when, really, I didn’t know what role we were playing,” remembers Barbara. “Who are we tonight?”

The pressure on the family only intensified when Colby returned to Vietnam in 1968. “My mother was at loose ends,” Carl recalls. “She lost the center out of her life. It was very hard for her.” For his part, he would watch the evening news and see the lovely villages of his boyhood being bombed and napalmed. His father returned home periodically with sensible-sounding explanations for what the U.S. was doing, but Carl couldn’t reconcile them with the chaos unfolding on TV. After the Phoenix Program became public, Barbara remembers, she and her husband were ostracized by his CIA colleagues who’d turned against the war. Because he was overseas, she shouldered the burden of caring for troubled Catherine. “My mother took on the suffering of my sister,” Carl remembers. “She would make it go away for my father. There couldn’t be any other way. Everything for the mission. . . . She hadn’t signed up for this. But she did it.”

In his voice-over, Carl Colby seems every bit as cool and contained as his father, but there’s an undercurrent of anger in The Man Nobody Knew: after nearly 40 years of marriage, Bill Colby stunned Barbara by asking her for a divorce, and in 1984 he married 40-year-old Sally Shelton, a career diplomat who’d served in the Carter administration. “I guess I would say he was a complicated person whom maybe I didn’t know as well as I would hope to think I did,” Barbara admits. Twelve years later, Bill Colby disappeared after going out in a canoe near his home in Rock Point, Maryland; his body was recovered nine days later, and his death was ruled a drowning accident, possibly brought on by a stroke or heart attack. Conspiracy theorists had a field day, but as Carl Colby reveals in the film, his father had phoned him two weeks earlier seeking “absolution” for the way he’d neglected Catherine. Bill Colby may have been a man nobody knew, but he may also have gotten to know himself too well.