The actor will play Alexander Litvinenko in 'Londongrad'
The show is based on Alan Cowell's book 'The Terminal Spy'. The book covers the bizarre events of 2006 where the former KGB agent-turned-defector and was mysteriously poisoned in London.
Litvinenko, who worked for the Russian Federal Security Service (FSB), fled to England in 2000. He became an author and outspoken critic of Vladimir Putin. He also worked as a counter-intelligence officer of British MI6. While in hospital, he helped solve his own murder by tracing a cup of tea back to a former comrade.
He died three weeks after ingesting the lethal radioactive isotope polonium-210.
As well as starring, Cumberbatch will serve as executive producer with his company Sunnymarch. David Scarpa, who has worked on 'The Man in the High Castle', will write the series.
Bryan Fogel, known for his Oscar-winning documentary 'Icarus', will direct the limited series.
Cumberbatch will return to work with HBO for the third time. He previously starred in 2013's 'Parade's End' and 2019's 'Brexit'. He received Emmy nominations for both projects.
'Londongrad' does not currently have a release date.