George Blake, a former British intelligence officer who worked as a double agent for the Soviet Union, has died in Russia. He was 98.

Russia’s Foreign Intelligence Service announced his death on Saturday without giving any circumstances of his death.

Russian President Vladimir Putin expressed condolences, hailing Blake as a “brilliant professional” and a man of “remarkable courage.”

Blake has lived in Russia since his daring escape from a British prison in 1966 and was given the rank of Russian intelligence colonel.

As a double agent, Blake passed some of the most coveted British secrets to the Soviet Union, including a Western plan to eavesdrop on Soviet communications from an underground tunnel into East Berlin.