Markus Wolf, the former head of communist East Germany's foreign intelligence service, has died at the age of 83, his family says.
Markus Wolf was known as the Man Without A Face
Wolf kept such a low profile that Western intelligence services did not have his picture.
But as a key figure in the feared Stasi security ministry, he was a highly influential figure in the Cold War.
He was interviewed by the BBC last year over his role as a journalist at the Nuremburg trials in 1945-6.
He said witnessing the evidence of the Nazis' crimes "influenced my later life because anti-fascism became the raison d'etre of my life".
He went on to head the Stasi's foreign intelligence division from the 1950s for three decades, running 4,000 spies and deeply infiltrating the West German government.
I hoped that after the Nuremberg Trials, there would be a time without war, aggression or crimes against humanity
One agent, Guenter Guillaume, got so close to West German Chancellor Willy Brandt that when he was unmasked the chancellor was forced to resign.
Wolf later described that as an "own goal".
On the fall of the Berlin Wall in 1989, Markus Wolf fled to Moscow, but later returned to the reunified Germany, where in May 1997 he was tried and found guilty of treason and kidnapping.
He was given a two-year suspended jail sentence.
In the final days of divided Germany, he said, the CIA asked him to defect to the US, with the offer of a home in California and a big salary.
He said he refused because he would never betray his agents.
After the Cold War, he released his memoirs, entitled The Man Without A Face, after the nickname he earned through being unrecognised.
Wolf was rumoured to have inspired the creation of "Karla", a master spy in John Le Carre's Cold War thrillers, but the author denied this.
Wolf's family said he died in his sleep overnight at his home in Berlin.