April 26 will mark 40 years since the Chernobyl disaster, still recognised today as history's most devastating nuclear accident.

In 1986, in the then Soviet-controlled country of Ukraine, reactor number four at the Chernobyl nuclear power plant suffered a calamitous explosion during a safety test gone fatefully wrong.

The engineers at the plant had wanted to assess what would happen during a power blackout, not realising the reactor was already extremely unstable.

The reduced power slowed turbines that transported water to the reactor, but with less water to cool the system, what was left quickly turned to steam - building up enormous amounts of pressure.

What followed was the largest uncontrolled radioactive release into the environment ever recorded for any civilian operation, affecting more than 3.5 million people and contaminating nearly 50,000 square kilometres of land.

Some 30 people died during the blast and in the subsequent months, 350,000 were evacuated, 5,000 children and adolescents were diagnosed with thyroid cancer, and poisonous radiation spread to lots of European countries - including many parts of the UK.

Investigations concluded that faulty protocols in the plant's design and poorly trained personnel were responsible for the explosion, which blew the 1,000-ton steel lid off the reactor - the same weight as three 747 passenger planes.

In 2019, the disaster was dramatised in the critically acclaimed HBO and Sky mini-series, 'Chernobyl', which documented the mistakes that led up to the explosion and the massive cleanup efforts that followed. 

From the scientists and engineers to the politicians and employees, ten key individuals played a crucial role in the unfolding tragedy and its aftermath.

Here's a look at what became of the figures central to the Chernobyl disaster:

1. Anatoly Dyatlov: The Deputy Chief Engineer

As the deputy chief engineer of the Chernobyl Nuclear Power Plant at the time of the explosion, Anatoly Dyatlov bore significant responsibility for the disaster. 

He supervised the ruinous test at the No. 4 reactor at the plant, resulting in the explosion that ultimately smashed its steel and concrete roof and spewed tons of radioactive rubble half a mile into the air. 

In preparation for the test, Dyatlov ordered the power to be reduced to 200 MW, which was lower than the 700 MW stipulated in the test plan - the reactor then stalled unexpectedly during preparations. 

After the incident, he was handed the majority of the blame by the authorities, having violated basic safety precautions.

'Anxious to complete a scientific experiment that had been ordered by Moscow, he bullied his subordinates into taking unnecessary risks,' the Washington Post wrote in 1992.

'His incompetence - combined with mistakes by other Chernobyl employees - led directly to the destruction of the reactor and the spewing of radioactive particles across a wide area of Europe.'

Although he was one of the few working at the reactor that night to have survived, he was later convicted of gross violation of safety regulations and sentenced to ten years in a Soviet labour camp. 

He was released in 1990 as part of a general amnesty for Chernobyl officials, and began the work of trying to clear his name - telling the Post that he and other operators were made scapegoats for the designers of a dangerously unstable reactor.

In his view, blame for the incident rested entirely with the leaders of the Soviet scientific establishment and their political patrons.

'I found myself confronted with a lie, a huge lie that was repeated over and over again by the leaders of our state and simple technicians alike. These shameless lies shattered me,' said Dyatlov. 

'I don't have the slightest doubt that the designers of the reactor figured out the real cause of the accident right away but then did everything to push the guilt onto the operators.'

Despite his declining health due to radiation exposure, he remained unrepentant until his death in 1995. 

The series creator of Chernobyl, Craig Mazin, maintains that Dyatlov in particular was a 'real bully', who later made statements that were not credible. 

2. Viktor Bryukhanov: The Director

As the plant's director, Bryukhanov faced similar charges to Dyatlov and was also sentenced to ten years in prison. 

He was released early after five years due to health concerns, and lived out his days in obscurity, haunted by the events of April 26, 1986. 

After prison, he eventually returned to government service in Ukraine to head the technical department in its Economic Development and Trade Ministry. 

His death in 2021, aged 85, was announced by a spokesman for the now-closed power plant. 

He had sustained several strokes since he retired in 2015 and was being treated for Parkinson’s disease.

Bryukhanov accepted professional responsibility for the disaster but rejected criminal liability, attributing the explosion to original technical flaws that had been designed by Moscow, the failure of higher-ups to provide the necessary equipment to measure radiation leaks, as well as bureaucratic red tape that divided responsibility between Communist Party apparatchiks and technocrats.

'My father came home after 24 hours, and it looked like he had aged 15 years,' Bryukhanov's son, Oleg, said in an interview for 'Under the Spell of Chernobyl', a 2020 Flemish TV series. 

The plant director insisted that he and other officials had been scapegoated as a result of 'a tissue of lies that distracted us from the real causes of the accident', during an interview with Russian magazine Profil in 2006. 

'You need to understand the real causes of the disaster in order to know in what direction you should develop alternative sources of energy,' he said.

'In this sense, Chernobyl has not taught anything to anyone.'

Bryukhanov waited until 4am - three and a half hours after the first explosions - to alert the authority nearest to the plant about the incident, according to historian Richard Rhodes in 'Arsenals of Folly', his 2007 book about the nuclear arms race.

Even then, he only reported roof fires, concealing the full extent of the disaster. 

3. Leonid Toptunov: The Senior Reactor Controller

A young and inexperienced engineer on duty during the night of the explosion, Toptunov suffered severe radiation burns and succumbed to acute radiation syndrome within weeks. 

He died aged 25 on May 14, 1986, and his family were later informed that his death was the only reason he was not prosecuted for the accident.

In 2008, Toptunov was posthumously awarded with the 3rd degree Order for Courage by Viktor Yushchenko, the then President of Ukraine. 

Engineer Oleksiy Breus entered the control room of the No. 4 reactor hours after the accident, becoming a witness to the world's worst nuclear disaster.

There, he spoke with Oleksandr Akimov, the shift leader at the reactor, and operator Toptunov - who were already irrevocably altered from the incident.

'They were not looking good, to put it mildly,' he told the BBC. 'It was clear they felt sick. They were very pale. Toptunov had literally turned white.'

'I saw other colleagues who worked that night. Their skin had a bright red colour. They later died in hospital in Moscow.'

He continued: 'Radiation exposure, red skin, radiation burns and steam burns were what many people talked about but it was never shown like this. When I finished my shift, my skin was brown, as if I had a proper suntan all over my body. My body parts not covered by clothes - such as hands, face and neck - were red.'

4. Yuri A. Laushkin: Senior engineer and atomic energy inspector at reactor No. 4  

Yuri A. Laushkin, a senior engineer and inspector at the reactor, was sentenced to two years in a labour camp for negligence and unfaithful execution of his duties.

He had pleaded not guilty.

According to Russian Life magazine, he died in prison.

The outlet claimed that Laushkin had carried out an inspection of the power station in 1983, and concluded that there were a number of problems with the reactor itself, that it was dangerous to work on, and soon a serious incident would occur. 

5. Vasily Ignatenko: The firefighter

Vasily Ignatenko was one of the very first responders at the Chernobyl plant in Pripyat. 

He was 25 years old when he tended to the blaze along with other firefighters at Chernobyl.

Ignatenko took to the building's roof and attempted to extinguish the open-air graphite fires atop that gave him his lethal dose of radiation.

He died, along with 27 other firefighters, due to radiation exposure less than three weeks later - but his historic contributions helped stop the crisis from becoming even worse. 

His wife, Lyudmila Ignatenko, detailed the build-up and the aftermath of her husband's death, revealing that the morgue could not put a suit or shoes on the firefighter, according to The Collector.

Ignatenko's radiation sickness had made it difficult to be buried properly, so he, as well as the other 27 first responders, was buried barefoot under layers of concrete and zinc to protect the public from his still radioactive body.

 6. Nikolai M. Fomin: Former chief engineer

Serving as the chief engineer of the Chernobyl plant, Fomin was convicted alongside Dyatlov and Bryukhanov to ten years in a labour camp.

After the accident, he fell ill with radiation sickness, which delayed the trial. 

He was found guilty of 'gross violation of safety regulations, creating conditions that led to an explosion' in July 1987.

After a three-week trial, most of it closed, Fomin received his sentence alongside other officials in a 90-minute summation in an improvised courtroom in the Chernobyl House of Culture.

The New York Times described how he dressed like the others, in a jacket and open-necked shirt, occasionally took off his eyeglasses under the glare of television lights and mopped his brow with a handkerchief. 

He accepted professional responsibility for the accident but denied criminal liability.

According to Newsweek, Fomin was released from labour camp early after a nervous breakdown and a suicide attempt.

His fate is unclear, but many speculate he succumbed to sickness due to exposure to radiation.  

7. Boris V. Rogozhkin: Shift Director 

Rogozhkin was shift chief at the reactor at the time of the explosion, and was sentenced to five years in a labour camp for violation of safety rules.

He also received a two-year sentence, to run concurrently, for negligence and unfaithful execution of duty.

He had pleaded not guilty. 

8. Alexander P. Kovalenko: Chief of Reactor No. 4 

Alexander P. Kovalenko, superintendent of the reactor, was sentenced to three years in a labour camp for violating safety regulations.

He pleaded not guilty at trial.

9. Boris Shcherbina: Deputy Chairman of the Council of Ministers of the Soviet Union 

A Soviet politician tasked with overseeing the government's response to the disaster, Shcherbina faced criticism for his handling of the crisis. 

He had arrived 18 hours after the explosion to find that none of the local ministers wanted to be responsible for the consequences of declaring the reactor dead. 

He refused to wear nuclear protection, and his first suggestion to contain the graphite fires was to pour water on them (which would have caused the fires to expand).

Buses had been waiting for 36 hours between Chernobyl and Pripyat, and still, citizens were not allowed to leave until the afternoon of April 27, when radiation levels had reached 180 to 300 milliroentgens per hour, according to The Collector.

Despite his initial denial of the severity of the situation, he later played a crucial role in the evacuation and containment efforts. 

Shcherbina passed away in 1990, his legacy shaped by his actions during Chernobyl. 

10. Maria Protsenko: Leading the evacuation after the Chernobyl disaster 

Maria Protsenko was the city's chief architect of Pripyat and a force to be reckoned with - she was known to carry a ruler with her as she assessed buildings, and would scold workers if they failed to be precise. 

On the night of April 26, 1986, Protsenko was one of the first to urge immediate evacuation. 

When Scherbina finally gave the order for residents to leave, Protsenko was put in charge of organising the evacuation.

She planned the escape of every person in every building and instructed waiting buses on where to take the citizens. 

Protsenko was the final person to leave the city only once she was satisfied that everyone else was safe.

The entire town of Pripyat, which had a population of 49,360 and lay only three kilometres from the plant, was completely evacuated 36 hours after the accident.

During the subsequent weeks and months an additional 67,000 people were evacuated from their homes in contaminated areas and relocated on government order.

She is still alive today and continued to live in Ukraine until 2022, when she and her family fled the country to Germany following Russia's invasion.