Any reader of Espionage novels over the last 60 years would surely have read at least one of his books. I have read an awful lot more than one of of his books. His novels set during the Cold War certainly seemed to have the ring of authenticity to me, and others, but he was always fairly coy about his real activities with MI6. Too me he seemed to struggle somewhat after the 'fall of the Wall' took a bit of the Raison d'être out of his work but that could be either just my imagination or due to his advancing age.
George Smiley would probably be the best known character he created - seemingly bland and boring but actually highly intelligent and completely merciless when necessary.
https://www.bbc.com/news/entertainment-arts-55297558