Andrei Sakharov is best remembered today as one of the foremost human rights advocates of the 20th century, winning the Nobel Peace Prize for his outspoken opposition to the Soviet Union's darkest totalitarian impulses. But he was also the conflicted "father of the Soviet hydrogen bomb" and helped accelerate an arms race that left humanity on the brink of annihilation.

Here is a pictorial look, using photographs from the Sakharov Archives and other sources, at how this brilliant and loyal physicist of the U.S.S.R. ultimately became its strongest and most celebrated voice of moral dissent.

Sakharov was born in Moscow on May 21, 1921, into a family that was firmly established as part of the city's intelligentsia.

Like much of his generation born just after the Bolshevik Revolution, the young Sakharov would have been imbued from an early age with communist ideas, such as social equality and justice.

But his early life at home also played a major role in shaping the man he was to become.

His father, Dmitry, was a respected physics teacher who wrote popular textbooks on the subject.

A principled and cultured man with a humanitarian outlook, he is believed to have had a profound impact on his son's intellectual development.

But his churchgoing mother, Yekaterina, and paternal grandmother, Maria Petrovna, were also a big influence.

Aside from "the Mongol cast of my eyes," Sakharov would subsequently credit them with bequeathing him "something of my character…a certain obstinacy, as well as an awkwardness in dealing with people that troubled me for much of my life."

Unusually for the time, he was homeschooled by his father and the experience seems to have been beneficial to his education. His exceptional scientific potential was recognized soon after he finally started attending formal classes in 1933 at 12 years of age. Five years later, he was accepted into the physics department of Moscow State University.

It was a turbulent time to be at college. Although a failed medical exam meant he wasn't called up to fight when Germany invaded the Soviet Union in 1941, Sakharov would have witnessed the destruction the conflict wreaked on his country, as he and other students were regularly drafted by authorities to help out during air raids, assisting with putting out fires, as well as loading and unloading supplies.

He and his classmates eventually ended up completing their studies in Turkmenistan, having been evacuated to Ashkabad (now Ashgabat) later that same year. Sakharov graduated with distinction from a fast-track program in 1942.

Upon finishing his courses, Sakharov suspended further studies to help out with the war effort. He ended up being assigned to routine scientific work at a munitions plant in Ulyanovsk.

Despite the humdrum nature of these tasks, he said later that he still managed to make "a number of inventions in the field of production control."

He also spent a lot of his free time writing academic articles on theoretical physics.

Although these were never published, he said the writing process gave him "the self-confidence so essential to every researcher."

Ulyanovsk is also where Sakharov met his first wife, Klavdia Vikhireva, who was working in the same plant as a laboratory technician.

They married in 1943 and had three children. The couple would remain together until Klavdia's untimely death from cancer in 1969.

In 1945, with the war coming to an end, he eventually returned to Moscow to study at the prestigious FIAN institute of physics, under the tutelage of Igor Tamm.

A renowned scientist who would later win the Nobel Prize for physics, the older man is seen as a major influence on Sakharov, who couldn't help being impressed by Tamm's academic outlook, which emphasized high levels of professionalism and moral standards in research.

The respect seems to have been mutual, with Tamm once noting that his young student "concentrates all his intellectual efforts on physics."

Although Sakharov seems to have enthusiastically embraced the rigors of his chosen discipline, he later recounted how he felt early stirrings of unease about the work he was doing when he heard the news of the first atomic bomb being dropped on Hiroshima in August 1945.

"I was so stunned that my knees practically buckled. There could be no doubt that my fate and the fate of many others, perhaps of the entire world, had changed overnight," he said. "Something new and terrible had entered our lives, a product of the greatest of the sciences, of the discipline I revered."

'The Grandeur Of The Task'

Despite his early misgivings about the direction in which his field of study was moving, he took only two years to complete his doctorate in particle physics in 1947, and quickly agreed to join his mentor a year later when Tamm was put in charge of a team of researchers tasked with designing a Soviet thermonuclear device.

At first, Sakharov assiduously applied himself to the development of the weapon. "We were all convinced that this work was of vital significance for the balance of power in the world," he said. "And we were fascinated by the grandeur of the task."

Many of the ideas that Sakharov came up with during his time at a nuclear research facility in the "secret city" of Sarov were considered crucial to the development of the U.S.S.R's first "true" hydrogen bomb, which was detonated in August 1955.

Sakharov's scientific work was well rewarded by the Soviets. He became the youngest person to be inducted into the Soviet Academy of Sciences at just 32 years of age. He also won a host of socialist awards and was afforded many of the same privileges as the Bolshevik elite, even though he politely declined to join the Communist Party.

Despite his success, however, Sakharov later said he was "becoming ever more conscious of the moral problems inherent in this work."

Increasingly haunted by the devastating power of the weapon he'd helped develop, Sakharov strongly opposed the overground testing of nuclear armaments after calculating that the fallout would eventually cause thousands of deaths for generations.

"The remote consequences of radioactive carbon do not mitigate the moral responsibility to future victims," he said. "Only an extreme lack of imagination can let one ignore suffering that occurs out of sight."

Perhaps one of the most pivotal events to have an impact on Sakharov's intellectual evolution came with the development of the so-called Tsar Bomba, the Tsar’s Bomb. Despite being plagued by doubts about the wisdom of building such a weapon, Sakharov toed the party line and helped test what is still considered to have been the most powerful device ever detonated.

If Sakharov thought the successful launch in 1962 of a weapon that unleashed 10 times the total amount of explosives used in World War II would satisfy the Soviet authorities' enthusiasm for ever more powerful weapons, he was to be bitterly disappointed.

WATCH: Declassified footage of the Tsar Bomba released in 2020 by the Russian state atomic energy agency, Rosatom, to mark the 75th anniversary of the country's nuclear industry:

The propaganda value of successfully testing such devices was too great a temptation. Despite Sakharov's strenuous objections, Soviet leader Nikita Khrushchev ordered the technically unnecessary detonation of another megaton bomb just a few months later.

It was the straw that broke the back of Sakharov's patience with the Soviet regime.

"A terrible crime had been committed, and I couldn't prevent it!" he said. "A feeling of impotence, unbearable bitterness, shame and humiliation overcame me. I dropped my face on the table and wept. This was probably the most terrible lesson of my life: You can't sit on two chairs."

Khrushchev's perceived betrayal seemed to galvanize Sakharov to push even harder for an end to the atmospheric testing of nuclear weapons. He is credited with playing a large role in finally convincing the Soviets to sign up to a partial ban in 1963.

He also became a much more open voice of dissent within the Soviet bureaucracy, making representations in defense of persecuted individuals and adding his name to calls for greater human rights protections.

In 1968, he finally ruptured his increasingly uneasy relationship with the regime he had once served so diligently when samizdat copies of an essay he wrote appeared under the title: Reflections On Progress, Peaceful Coexistence, And Intellectual Freedom.

It soon made its way to the West and was published in The New York Times, causing quite a stir with its impassioned plea for all of humanity to jointly tackle the "grave perils" it was facing, such as nuclear and ecological catastrophe.

Naturally, the nomenklatura didn't take kindly to someone they viewed as one of their own sharply criticizing their repression of dissidents, while also calling for the universal adoption of a more democratic socialism that respected the human rights of each individual.

Sakharov was quickly removed from all military programs and "relieved" of the elite privileges he had enjoyed.

Over the next few years, with his scholarly work confined to the study of fundamental physics, he became increasingly focused on political activism, coming out publicly in support of human rights and other causes, much to the ire of the Moscow authorities.

It was while attending a trial of rights activists in 1970 that he met Yelena Bonner, a fellow dissident with whom he struck up an immediate rapport. They would end up marrying two years later and remain together until Sakharov's death.

Although Sakharov's star may have been waning in Moscow, he was soon to become a household name in the West and one of the most visible and vocal Soviet dissidents.

He and Bonner's tireless work for human rights soon established the couple as a focal point of opposition to the regime, and their Moscow flat and dacha became de facto clearinghouses for rights groups.

While other dissidents were routinely picked up by the authorities or forced into exile, Sakharov's status as a celebrated state scientist helped ensure that he and his wife remained free to write and give interviews to foreign correspondents, although they routinely faced harassment from the KGB and denunciations in the press.

When Sakharov's burgeoning reputation as "a spokesman for the conscience of mankind" saw him being awarded the Nobel Peace Prize in 1975, the Soviets were so irritated that they refused him permission to travel to Oslo to receive the accolade.

As luck would have it, Bonner had been allowed abroad at the time for eye surgery in Italy, and she accepted the honor on his behalf.

In his acceptance speech, read by Bonner in Norway, he expressed his "hope in a final victory of the principles of peace and human rights."

Somewhat pointedly, he also dedicated the award to other dissidents, saying his prize was to be "shared by all prisoners of conscience in the Soviet Union and in other Eastern European countries as well as by all those who fight for their liberation."

Although his international standing as a Nobel laureate offered him some protection from persecution, Sakharov's dissident activities eventually wore out Moscow's patience when he publicly condemned the Soviet invasion of Afghanistan in 1979 and supported a boycott of the Moscow Olympics.

Early in 1980, he was snatched from the streets of Moscow by the authorities and banished without trial to the city of Gorky, some 400 kilometers east of the capital. Bonner was packed off to join him in internal exile four years later.

If the Soviets thought the move would silence Sakharov, they were sorely mistaken. He quickly became a cause célèbre as Western scholars campaigned in the international media on his behalf.

A number of hunger strike protests helped consolidate his status abroad as a symbol of the opposition. It's said that many within the communist elite were also influenced by the principled stand he was taking.

​As the increasingly open atmosphere of the perestroika era quickly gained momentum, Sakharov's writings were crucial in providing an intellectual framework for the reform movement.

With Soviet leader Mikhail Gorbachev's glasnost policies beginning to take hold, Sakharov was eventually released in December 1986 and he returned to Moscow amid much fanfare.

If the politburo had hoped Sakharov's freedom would help lend legitimacy to the reforms they were attempting to implement, he himself continued to push relentlessly for greater transformation, even issuing a call for the release of other political prisoners not long after his triumphant return to the capital.

Despite declining health, Sakharov spent the next few years working tirelessly for more change, taking advantage of the greater climate of openness to get himself elected to the Congress of People's Deputies, where he pushed constantly for constitutional reform and an end to the Communist Party's monopoly on power.

By this time, he and Bonner were the most recognizable faces of the Soviet opposition, both at home and abroad.

Their celebrity status enabled Sakharov to travel outside the country to help drum up international support for greater reform in the U.S.S.R. He had the ear of numerous world leaders and influencers.

This late flurry of activity took its toll, however, and he died suddenly of heart failure in December 1989, just three years after his release from internal exile.

Although he lived long enough to see the fall of the Berlin Wall, Sakharov's tragic demise arguably came just when his country needed him most.

A 'Moral Symbol'

Czechoslovakia's first postcommunist president, former dissident Vaclav Havel, perhaps caught the prevailing mood when he told reporters it was "a real tragedy for the Soviet Union that Sakharov died, because otherwise very soon he might have become president there."

It's a source of endless speculation as to what might have happened if the man Havel described as "the only integrating personality" in the U.S.S.R. at the time had lived to see its collapse.

Certainly, the version of his country that emerged from the ruins of the Soviet Union is a far cry from "the open pluralistic society with unconditional respect for basic civil and political human rights" that he envisioned.

But the ideals he espoused still have a voice in many parts of the world, not least in contemporary Russia. Rights organizations like Memorial and the Moscow Helsinki Group, which he played a pivotal role in establishing, are still as relevant and important today as they were decades ago.

His legacy also lives on in the form of the Sakharov Prize for Freedom of Thought, a prestigious award established with his blessing in 1988 by the European Parliament to honor individuals and organizations defending human rights and fundamental liberties.

Not surprisingly, the list of winners of the Sakharov Prize reads like an honor roll for conscientious dissent, including the likes of South Africa's Nelson Mandela, Pakistani girl's education activist Malala Yousafzai, Memorial, Ukrainian filmmaker Oleh Sentsov, and the current protest movement in Belarus.

At a time when "authoritarian regimes and populist forces undermine fundamental freedoms and question the principle of human rights," says European Parliament President David Maria Sassoli, "the moral symbol represented by Andrei Sakharov constitutes a source of inspiration for all those who fight for democratic principles."