George Blake

An MI6 officer who decided to work for the Soviet Union after being captured in the Korean War, Blake did damage on two fronts. He is said to have exposed some 40 British agents in Eastern Europe and the Middle East, some of whom were executed or imprisoned, and he betrayed the CIA's Berlin tunnel, built to tap Soviet lines, which he called his greatest exploit. Convicted in 1961, he received 42 years, then the longest sentence in British legal history. The ending is the part that sounds invented: in 1966 he escaped from Wormwood Scrubs with help from men he had met in prison and reached Moscow, where he died in 2020 at 98.