Capgras delusion is a disorder in which an individual believes that a friend or family member has been replaced by an identical imposter. It is most commonly found in persons suffering from schizophrenia, but can also be found in those suffering from dementia. The delusion is named after Joseph Capgras, a French doctor who first described the experiences of one of his patients, a woman in 1923 who believed that her family members were replaced by other people.