Fregoli delusion is a psychological condition where a person believes that different people are actually a single individual who changes appearance or disguises themselves. This delusion often leads to the mistaken belief that this person is following or plotting against them, causing significant distress. The condition is named after the Italian actor Leonido Fregoli, known for his quick changes in character and appearance. Fregoli delusion is often associated with other mental health disorders, such as schizophrenia or bipolar disorder, and can be challenging to treat, requiring a comprehensive approach that may include therapy and medication.