Peter Whybrow was a psychiatrist, neurologist and writer who was born on 13 June 1939 in Hatfield, UK and died on 25 August 2025 of cancer at the age of 86 in Waitsfield, Vermont, USA.[1] His main research focused on the metabolic role of thyroid hormones in the adult brain and their use in the treatment of mood disorders, especially bipolar disorder.[1][2] He proved that some patients with affective disorders have abnormalities of thyroid metabolism in the brain, which negatively affects the course of the disease.[1] In the 1970s, he developed the Chronorecord, an electronic daily self-report system for monitoring the course of illness and treatment, which has been translated into six languages and is used in collaborative studies in Germany, Canada, Australia, and Great Britain.[1] He served as the Judson Braun Distinguished Professor at the UCLA David Geffen School of Medicine, from 1997 to 2020 he was executive chair of psychiatry and director of the Semel Institute for Neuroscience and Human Behavior.[1][2] He was an international authority on depression and manic-depressive illness, author of numerous scientific papers and books such as A Mood Apart and American Mania.[1][2][3] He was a founding member and fellow of the Royal College of Psychiatrists and a fellow of several American institutions.[2][3]