British and US secret services obsessed over the birth of Charlie Chaplin in a fit of Cold War paranoia that the communist-sympathising star might have had Russian-Jewish roots.
Newly declassified MI5 files show US intelligence thought his real name may have been Israel Thornstein and that after his birth Chaplin's parents fled the Russian pogroms in which Jews were persecuted at the turn of the 20th century.
They also thought he may have been born in France.
The files have been made public by the National Archives.
US intelligence agencies sent several requests to their British counterparts to investigate Chaplin's birth.
"The various directories show Chaplin's name to be CHARLES SPENCER CHAPLIN, born 16.4.1889, London, the son of Charles Chaplin and his wife Hannah (professionally known as Lily HARLEY)," read a memo from one British secret service official to the Americans.
"I have searched at Somerset House the relevant indexes of births for England and Wales but could find no record of any person of the above-mentioned surnames with the Christian name Charles, Charles Spencer or Israel born 16.4.1889.
"It would seem that Chaplin was either not born in this country or that his name at birth was other than those mentioned."
Chaplin's file contains records of his relationships with communist groups and organisations, as well as details of any money he sent them.
There are also press cuttings and personal documents, including telegrams and letters sent to Chaplin that MI5 had got hold of, as well as information about planned trips to the Soviet Union.
Among the 86 declassified MI5 files in the National Archive release are documents on Nobel prize-winning chemist Marie Curie's son and daughter, Frédéric Joliot-Curie and Irène Joliot-Curie, both active communists and atomic scientists.
They were monitored by MI5 while they stayed in Britain.
Another file details the Nazi plot to flood Britain with forged banknotes to push up inflation and destabilise the economy during the war.