Mervyn Peake (1911-1968) was an accomplished British artist, poet, novelist, and playwright. He was a prolific and talented illustrator and wrote hundreds of poems, 4 novels, and several plays. His exceptional career was prematurely ended by a neurodegenerative illness variously ascribed to Alzheimer disease, Parkinson disease, or postencephalitic parkinsonism. However, a detailed review of biographical accounts produces substantial evidence in support of a probable diagnosis of dementia with Lewy bodies, a clinical entity remaining undiagnosed outside specialty dementia clinics. Peake developed signs of parkinsonism and insidious cognitive decline during his fifth decade. A breakdown in his writing style has frequently been cited as reflecting his encroaching dementia. Visual hallucinations are portrayed in sketches, and together with paranoid delusions are apparent in poetry composed during his illness. His deterioration was progressive and punctuated by well-described episodes of confusion and psychosis. His occasional preservation of insight is poignantly captured in drawings of figures with dunce caps or pointed heads, often with expressions of fear and apprehension etched with an economy of strokes. Peake spent his final years in various psychiatric institutions but continued to exhibit lucid intervals even late into his illness. His tragic deterioration remained undiagnosed at the time, but in retrospect, his progressive dementia with parkinsonism, visual hallucinations, and marked cognitive fluctuations likely represents one of the earliest recognized historical cases of dementia with Lewy bodies.