Ralph Ineson, who played the former Soviet General Nikolai Tarakanov, gave several interviews about the series, and these drew great interest when they were published in Russia. Although Tarakanov objected to a few small details, he generally praised the series and its handling of the events and stated that he was portrayed accurately. Tarakanov, who was 85 in 2019, is battling a chronic illness caused by radiation exposure during his time at Chernobyl.
Lyudmila Ignatenko, played by Jessie Buckley, is the pregnant wife of firefighter Vasily Ignatenko (Adam Nagaitis), who died in the disaster, and she was the subject of the 2001 Swedish documentary "Ljudmilas röst". The young couple, who married in 1983, had planned to travel to Belarus on that fateful morning, 26 April 1986, to visit Vasily's family. At the time the series aired, Lyudmilla was living in Ukraine with her son after losing her husband and daughter to radiation poisoning.
In the Blu-Ray special features, actor Jared Harris explains the significance of a scene in episode 2: the character Valery Legasov lies to an anxious couple at the hotel bar, telling them there is no problem at Chernobyl. According to Harris, this moment is the turning point at which Legasov ceases to be an innocent bystander and begins to feel directly responsible for the consequences of the disaster.
While most of the main characters portray real people, Ulana Khomyuk is a fictional character representing the dozens of Soviet scientists who worked to investigate and solve the Chernobyl disaster. This character was written to "honour their dedication and their service to truth and humanity".
The role of Valery Legasov, played by Jared Harris, was originally considered for Daniel Day-Lewis; however, Day-Lewis announced his retirement from acting a month before the miniseries was announced. The two had worked together on the 2012 film Lincoln, with Harris playing General Ulysses S. Grant and Day-Lewis playing Abraham Lincoln.
Emily Watson and Stellan Skarsgård played a couple in the 1996 film Breaking the Waves, which was a breakthrough for both of them. This film is the only other production in which the two have appeared together.
Michael McElhatton, Jamie Sives, Josef Altin, James Cosmo, Donald Sumpter and Ralph Ineson are names who appeared in Game of Thrones (2011).
Stellan Skarsgård had previously played a Soviet submarine captain in The Hunt for Red October (1990), which dealt with the Cold War era.
Jared Harris (Valery Legasov) and Adam Nagaitis (Vasily Ignatenko) had worked together in season 1 of The Terror (2018), as Francis Crozier and Cornelius Hickey respectively.
Part of the cast is connected to the Harry Potter series: Adrian Rawlins played Harry's father James Potter in the seven films beginning with Harry Potter and the Philosopher's Stone (2001) and ending with Deathly Hallows: Part 2 (2011). Paul Ritter was Eldred Worple in Harry Potter and the Half-Blood Prince (2009). Ralph Ineson played Amycus in the same film. Although Jared Harris did not appear in the films, he is the son of Richard Harris, who played Albus Dumbledore in the first two Harry Potter films; also, Sam Troughton, who played Aleksandr Akimov, is the cousin of Harry Melling, who played Dudley Dursley in the Harry Potter series.
Barry Keoghan's character, Pavel, has the same name in both this miniseries and the 2017 film Light Thereafter.
Donald Sumpter appeared in both K-19: The Widowmaker (2002) and the Chernobyl (2019) miniseries. Both productions revolve around a nuclear disaster.