From 1969 onward, Kissinger, a former Harvard professor and onetime advisor to New York’s liberal Republican governor, Nelson Rockefeller, served as Nixon’s national security advisor; after September 1973 he also served as Secretary of State. Together, Nixon and Kissinger notched a series of foreign policy triumphs, including withdrawing hundreds of thousands of American troops from Vietnam, broaching a new era of détente with the Soviet Union, and establishing diplomatic relations with the People’s Republic of China.

It was history’s cruel joke on both men that while their reputations would be forever linked, neither seemed to like the other very much. “I don’t trust Henry,” Nixon once confided to an associate, “but I can use him.” For his part, Kissinger called his former commander-in-chief a “lonely, tortured and insecure man,” both “monomaniacal” and “flawed.”

It was not a match made in heaven. But it worked, and for better or worse, it fundamentally changed the course of American foreign policy in the height of the Cold War.

Born in Bavaria in 1923, Kissinger fled Nazi Germany in 1938 with his family and relocated to Washington Heights, a neighborhood in northern Manhattan that was host to a vibrant German-Jewish community. After serving in the United States Army during World War II, he used his G.I. Bill benefits to attend Harvard University, where he earned his B.A. and Ph.D. in political science.

With a tireless work ethic and brash intellect, Kissinger made a strong impression on his academic advisors and fellow graduate students. His relentless charm offensive — a precursor to later displays of the same extreme obsequiousness that would become the stuff of White House legend — prompted some of his colleagues to dub him Henry Ass-Kissinger. “One heard an enormous amount about him,” a graduate school peer later remembered, “what an extraordinarily arrogant and vain bastard he was.” Kissinger’s doctoral dissertation, entitled “Peace, Legitimacy and Equilibrium: A Study of the Statesmanship of Castlereagh and Meternich,” was a bold reinterpretation of the Congress of Vienna of 1814-15, which saw the major European monarchies re-impose continental stability in the aftermath of the Napoleonic wars at the cost of stifling national and liberal forces unleashed by the French Revolution. Arguing for “stability based on an equilibrium of force,” Kissinger’s dissertation betrayed a decidedly conservative realpolitik — a concern with order over justice that, his protestations to the contrary notwithstanding (“Metternich is not my hero!” he swore time and again), informed his later career as an architect of American foreign policy.

After earning his Ph.D., Kissinger rose steadily up the ranks as a Harvard faculty member, from instructor to tenured professor. He also served as a consultant to the RAND Corporation, the State Department, and Nelson Rockefeller. By the eve of his selection as national security advisor, Kissinger was widely regarded as a thoughtful voice on arms policy and a skeptic on the Vietnam War. But he had little applied political or governmental experience.

In late 1968 he wrote an article for Foreign Affairs which argued that the United States had probably overestimated the stakes in Southeast Asia early in its involvement there. He essentially suggested working out a formula by which the U.S. could pull out of Vietnam, so long as the American-backed government in Saigon remained viable for a reasonable length of time. This strategy was in line with Kissinger’s private ruminations in 1968, when he repeatedly told colleagues and students that America should aim for a “decent interval” of about two years between a U.S. withdrawal and a Communist takeover in South Vietnam.

At first, it was hardly clear that Kissinger’s Vietnam policy made him a good fit for the Nixon administration. In the years immediately preceding his election as president in 1968, Nixon had positioned himself as an outspoken hawk, certainly more strident than his incoming national security advisor. But as president, Nixon faced hard realities. When he took office the war was costing American taxpayers roughly $30 billion annually. The United States had already lost almost 40,000 soldiers, marines and airmen and still had 536,000 troops stationed in southeast Asia. Vietnam had become an unaffordable and tragic excess of the Cold War — one that Nixon was determined to draw to a close. In that sense, Kissinger was a natural fit as his national security advisor.

For all the hours they spent huddled together in close conversation or plotting strategy over the telephone, Kissinger and Nixon enjoyed what might be generously described as a highly dysfunctional relationship. Sharing both a common distrust of each other and a general paranoia about the rest of the world, both men eavesdropped on themselves — Nixon, by recording his own Oval Office phone calls, and Kissinger, by planting an aide at a silent, “dead key” extension and having him transcribe or take notes on his phone conversations.

Kissinger routinely entertained his NSC staff by referring to Nixon as “the madman,” “our drunken friend,” and “the meatball mind,” warning that “if the president had his way, there would be a nuclear war each week!” When Nixon broke into angry rants or slurred his words badly — something he generally did when he consumed more than two cocktails, which as his presidency wore on, was more often than not — Kissinger would encourage aides to listen in on the dead-key extension and share in the spectacle.

Pete Peterson, then a Nixon White House aide, noted that “the contrast was striking between how [Kissinger] talked about Nixon to his friends and how he acted in Nixon’s presence.” On the Georgetown dinner party circuit, he could be merciless in his assessment of the president, but in their direct exchanges, Kissinger brought new meaning to sycophancy. “He was obsequious naturally,” John Ehrlichman later claimed. “He would lard things unbelievably. Nixon would make an outrageous statement, and instead of humming and staring at the ceiling like I would do, Kissinger would eagerly rumble in with, ‘Yes, Mr. President, your analysis is absolutely correct and certainly very profound.’ I would cringe.”

Kissinger showered Nixon with praise, calling him “genuinely heroic,” telling him that his performance with the Soviet ambassador was “extraordinary! No president has ever laid it on the line to them like that.” When Nixon delivered a major address on Vietnam in 1971, Kissinger told him that “free people everywhere will be forever in your debt. Your serenity during crises, your steadfastness under pressure, have been all that have prevented the triumph of mass hysteria.” Sensitive to his reputation as a world-class sycophant, Kissinger often tried to defuse criticism with dry humor. When his direct line to the Oval Office lit up during a meeting with a reporter, Kissinger quipped, “I don’t want you to get the wrong idea just because I was on my knees when I answered the phone.”

For his part, Nixon seemed to enjoy unnerving his national security advisor. “Nixon would talk about Jewish traitors,” recalled Ehrlichman, “and he’d play off Kissinger, ‘Isn’t that right, Henry? Don’t you agree?’ And Henry would respond, ‘Well Mr. President, there are Jews and then there are Jews.’” Once, when Nixon phoned with a particularly crude rant, a top NSC aide, asked, “Why didn’t you say something?” “I have enough trouble fighting with him on the things that really matter,” Kissinger sighed. “His attitudes toward Jews and Blacks are not my worry.”

Years later, Kissinger bumped into John Ehrlichman on the street and said, “Sooner or later, those tapes are going to be released, and you and I are going to look like perfect fools.” Ehrlichman disagreed. If anyone was going to seem foolish, it was Kissinger.

But during their time in office, the two men became close collaborators. Despite his roots as a Cold War hawk, Nixon was fundamentally a pragmatist, both in foreign and domestic politics. He also shared Kissinger’s detached and fundamentally amoral approach to foreign policy. “If I had to choose between justice and disorder, on the one hand, and injustice and order, on the other,” Kissinger had said during his days as a graduate student, “I would always choose the latter.”

In their approach to matters as far and wide as China (Nixon, the hawk, normalized relations) and Israel (the U.S. came to Israel’s rescue during the Yom Kippur War but forced the Jewish state to forego a total victory in order to placate oil-producing Arab states), they chose order — or the illusion of order — over dogma or morality.

Nowhere was that more true than Vietnam, where through a process of “Vietnamization,” they drew down troop levels to less than 25,000 within four years but also launched a ruthless bombing campaign whose death toll ranged as high as the hundreds of thousands.

The more influence he enjoyed with the president, and the greater his celebrity grew among Washington’s Georgetown elite, the more outrageous Kissinger became in his conduct. Ever the college professor, he was notorious for running hours behind schedule and keeping a chaotic office. “In the first year it was like a Moroccan whorehouse, with people queuing up outside his door for hours,” remembered one of his senior assistants. He screamed at his staff, hurled papers and books at them, berated them in public.

Ever jealous of prerogatives and power, he forbade them to use the White House mess, thus cutting off their independent access to key White House aides. Nixon aide Bryce Harlow’s office stood between Kissinger’s and Haldeman’s and contained the only private bathroom on the ground floor of the West Wing, other than the president’s. According to one White House insider, after a brief absence from Washington, Harlow returned to find the door to his washroom plastered over. Kissinger had ordered workmen to cut a new entrance from his own suite.

The charge most commonly directed at Kissinger was deceit. “Kissinger doesn’t lie because it’s in his interest,” said a former aide. “He lies because it’s in his nature.” Ron Nessen, who later served as Gerald Ford’s press secretary, added that “the Kissinger trait that troubled me most was his lack of commitment to the truth as a matter of morality. Kissinger bent the truth to serve what he believed were worthwhile foreign policy maneuvers.” Part of this reputation for duplicity was Kissinger’s desire to be all things to all people. However disparaging he may have been of the ivory tower when in Nixon’s presence, he had committed the better part of his life to Harvard, and he cared deeply what his Cambridge colleagues — many of them Cold War liberals who had turned against the war, and who held no brief for Richard Nixon — thought about him.

Likewise, he assiduously courted Washington’s opinion-making elite — the journalists, wise men and socialites who gravitated to the Georgetown dinner circuit. “We knew Henry as the ‘hawk of hawks’ in the Oval Office,” Bob Haldeman wrote. “But in the evenings, a magical transformation took place. Touching glasses at a party with his liberal friends, the belligerent Kissinger would suddenly become a dove — according to the reports that reached Nixon.” Frank Shakespeare, who ran the U.S. Information Agency, noted with less derision that “Kissinger can meet with six different people, smart as hell, learned, knowledgeable, experienced, of very different views, and persuade all six of them that the real Henry Kissinger is just where they are.”

Some of this criticism was fair. As David Keene, who served as Spiro Agnew’s chief of staff, noted, Kissinger “had one line for liberals, one for conservatives, and all the time he’d swear you to secrecy — ‘what I’m about to tell you is the highest-classified information’ — and he’d give you some bullshit, and he’d give somebody else the opposite.” On the other hand, for all his strategic flexibility and posturing, Kissinger genuinely reached out to war critics, going so far as to initiate friendships with prominent peace activists.

Unlike most members of Nixon’s inner circle, Kissinger, ever the Harvard scholar, welcomed intellectual dissent and encouraged his staff members to challenge both conventional wisdom and administration doctrine. In the end analysis, Kissinger often tailored his policy recommendations to Nixon’s personality. But when it came to assimilating the work and opinions of his staff, he did listen.

At about 9 p.m. on Wed., August 7, 1974 — a day and a half before he left the presidency — Nixon summoned Kissinger to the Lincoln Sitting Room, a small alcove on the second floor of the southeast side of the White House. It was clear to Kissinger that Nixon had been drinking heavily.

“Will history treat me more kindly than my contemporaries?” the president asked his Secretary of State. Kissinger nodded yes and joined Nixon in a long recitation of the administration’s foreign policy achievements. Weeping into his cocktail glass, Nixon asked Kissinger why life had dealt him such a terrible blow.

Around 10:30, the meeting ended. Escorting Kissinger out of the room, the president stopped in front of the Lincoln Bedroom and beckoned him inside. “Henry,” he pleaded, “you are not a very orthodox Jew, and I am not an orthodox Quaker, but we need to pray.” Kissinger would rather have not, but when the president dropped to his knees, he had little choice but to follow. When the president seemed finished with his prayers, Kissinger began slowly to rise to his feet. But Nixon remained low to the ground, sobbing and pounding his fists against the bedroom carpet, crying “What have I done? What has happened?” Kissinger crawled over to his grief-stricken leader, embraced him in his arms, and helped him to his feet. Several interminable moments passed before Nixon regained his composure.

At least, that’s how Kissinger remembered the story, according to journalists Carl Bernstein and Bob Woodward, who interviewed sources in whom the Secretary of State confided shortly after leaving Nixon’s side.

The history of academics-turned-White House aides is checkered. Franklin Roosevelt packed his White House with professors, many of whom proved masters of Washington, D.C., politics and federal bureaucracy. Other academics like Arthur Schlesinger, Jr., and Eric Goldman, who worked in the Kennedy and Johnson administrations, respectively, were disappointed to find themselves window dressing — marginal figures whose presence on staff was more ornamental than substantive.

A force of nature, Henry Kissinger willed himself to relevancy. For two years he even managed to occupy the positions of national security advisor and Secretary of State. And then, thanks in no small part to the entry he gained through his partnership with Nixon, Kissinger stayed on as Secretary of State for President Gerald Ford, outlasting his mentor at the highest ranks of government. In his post-governmental life, he became a corporate board member, strategic advisor to companies and presidents and prolific writer, sought after for his advice even as his mentor lived out his days largely in disgrace.

None of it would have been possible but for the unique and arguably singular relationship he forged with Nixon.