Solitary Persons? describes the autism theories of George Frankl (1897-1975), Hans Asperger (1906-1980) and Leo Kanner (1894-1981). These medical doctors were among the first to work with autistic children. Frankl’s role in the history of autism was discovered in 2015 and is clarified here. Asperger and Kanner are well-known founders of autism research, but this dissertation presents new discoveries about their work and a new interpretation of their work as a whole. Frankl, Asperger and Kanner each had a metaphor for autistic children. Frankl used a ‘prisoners’ metaphor. He believed that autistic children, even when they are with other people, are stuck in a solitary state: they do not express how they feel or notice such expressions in others. Asperger’s metaphor for autistic children was that they are ‘machines’. He believed that autism involves an overdevelopment of intellect and of independence from the environment. Kanner wrote that autistic children are ‘barometers’, sensitive to the emotional climate in their home. He believed that autism is an emotional disorder that affects and is affected by the whole personality. Contemporary theories of autism usually explain only some of its symptoms. This conceptual-historical study is a search for older theories of autism that conceptualise its entire symptomology. Frederik Boven (b. 1981) is historical psychologist and philosopher. He has a PhD degree in psychology. At age 34 he was diagnosed with Asperger’s syndrome. He is director of Autism Digital (Autisme Digitaal), a Dutch autistic-led foundation that aims to disperse knowledge about autism in adulthood.