Alicia Shepard is the author of “Woodward & Bernstein: Life in the Shadow of Watergate.”

The Watergate scandal generated many household names: Washington Post reporters Bob Woodward and Carl Bernstein, Judge John J. Sirica, Nixon aide John Dean.

But someone often left out of the popular narrative is the person responsible for ensuring that President Richard Nixon left office.

His name is Alexander Butterfield.

On July 13, 1973, Butterfield told Senate investigators that Nixon had a taping system.

It wasn’t known then just how damning the tapes would be. But they would prove that Nixon had tried to cover up the burglary of Democratic headquarters at the Watergate hotel on June 17, 1972.

As White House deputy chief of staff, Butterfield managed the president’s West Wing schedule. He knew that in February 1971 a voice-activated taping system was installed in the Oval Office and other areas because he ordered the Secret Service to do it. Only a handful of people knew of its existence. And if not for Butterfield’s revelation, the system might have stayed secret.

In May 1973, when the Senate Select Committee on Presidential Campaign Activities published a list of people it intended to interrogate, Butterfield wasn’t on it. “I was sort of surprised but relieved since I had nothing to do with Watergate,” Butterfield told me in 2002, as I researched a book.

Butterfield, now 86, had left the White House in December 1972 and gone on to head the Federal Aviation Administration. When the committee list was published, he thought he was safe. He knew he possessed a valuable secret, but he was also a loyal Republican with no intention of squealing.

Then came a phone call. Senate investigators wanted to know what, if anything, he knew. He was invited to a standard pre-interview on Friday, July 13.

Before he went, he had a heart-to-heart with his wife, Charlotte.

“I didn’t want to lie,” Butterfield recalled. “I never entertained the thought of lying. But I knew what a big secret this was to Nixon.”

He and Charlotte agreed that Butterfield would volunteer nothing; he’d only answer a direct question. “If the investigators asked me an indirect or fuzzy question,” Butterfield said, “I was justified in giving an indirect, fuzzy answer.”

After a few hours of questions, Butterfield felt he was in the clear. Then the inquiries turned to the president’s Dictaphone. Late at night, Nixon would dictate letters into a recorder for his secretary, Rosemary Woods, to type the next day.

“Were there ever any recording devices other than the Dictaphone system you mentioned,” he recalled being asked.

The session was not recorded, which has led to debate about who asked the question. Some say it was Democratic investigator Scott Armstrong, but many, including Butterfield, say it was Republican investigator Donald Sanders.

Butterfield froze. This was a direct question. He hesitated, took a deep breath and answered, “Yes.”

The room fell silent. The tension was palpable. “They were young,” Butterfield told me. “They were ecstatic. I said, ‘Wait a minute. Let’s be serious. I know this information I gave you is monumental. Let’s think this through.’ ”

But it was too late. The investigators instantly understood the significance of Butterfield’s answer.

The following Monday, with TV cameras trained on him, Butterfield testified to the Senate select committee that Nixon had a taping system in the Oval Office. Most quickly realized that the tapes could be revelatory about the break-in.

“Frankly, I don’t like being known as the man who revealed the existence of the tapes,” Butterfield told me. “It makes it appear that I ran full tilt to the Watergate committee and told them eagerly and breathlessly the very information that Nixon considered top secret. That was not the case. I was facing a true dilemma: I wanted very much to respect Nixon’s wishes and at the same time to be cooperative and forthright with the congressional investigators. The wording of their questions meant everything to me. And when Don Sanders, the deputy minority counsel . . . asked the $64,000 question, clearly and directly, I felt I had no choice but to respond in like manner.”

Nixon fought as hard as he legally could to hold on to the tapes. He even ignored suggestions that he burn them. Nixon’s lawyers argued before the Supreme Court that the tapes were protected by executive privilege. On July 24, 1974, the justices decided differently. By a vote of 8 to 0 — Justice William Rehnquist recused himself — Nixon was ordered to turn over the tapes.

Fifteen days later, the president of the United States resigned.

“If you didn’t have the tapes, then there would have been an ambiguity about all of this,” Woodward said at a Washington conference in April. “It’s the clarity of the tapes. The people who listened to them, particularly Republicans on the House Judiciary Committee, would not only deal with the substance, but it was the rage that Nixon would get in about small things and the indifference to the law.”

His mother thought Butterfield a hero. Butterfield, however, knew he had burned bridges. Eight months later, he was out as chief of the FAA.