My head is starting to spin from all of these mental conditions, so I will keep this brief. This delusion is almost the opposite of Capgras — it is the believe that two different people are actually the same person in disguise. Like Capgras, it seems to relate to some breakdown with the minds ability to recognize faces.
Fregoli’s, interestingly enough, is not named after the physician who first noted it, like many other illnesses are. The illness was first reported in 1927 by two doctors, Courbon and Fail, who told the story of a woman who believed that she was pursued by Sarah Bernhardt and another famous actress, who could take control of anyone’s body and make her do things against her will. Fregoli is a reference to the Italian actor Leopoldo Fregoli, who was a famous quick-change actor of the time.