Aaron Temkin Beck (known to friends and colleagues as Tim) was born in Providence, Rhode Island, on 18 July 1921, the youngest of four children of Russian Jewish immigrants. Beck celebrated his centenary with a Zoom birthday gathering, during which he received a message from the Dalai Lama, who told Beck that ‘you have lived a truly meaningful life and continue to be an inspiration to us all’. Sadly, Beck died on 1 November 2021. Although much has been and will be written about Tim, this brief article offers an appreciation of one of the world's leading researchers in psychopathology and the ‘father of cognitive–behavioural therapy’.

It is sometimes forgotten that, after obtaining a medical degree from Yale in the years just after the Second World War, Beck was considering a career in neurology (attracted by the high degree of precision of that discipline). However, after a placement in psychiatry, he became fascinated with psychoanalysis. Unlike his peers, Tim didn't just practise psychoanalysis, he researched it. He began a series of carefully conceived studies that aimed to validate Freudian psychoanalytic constructs but ultimately led to the development of a new theory of depression. Like Kraepelin, Beck was an acute observer of mental states, but like Jaspers he placed great value on understanding the cognitive and emotional content of psychopathology from the patient's perspective. His critical contribution was discerning that the way we feel and behave is understandable in the context of consciously accessible beliefs. Beck successfully translated his understanding of the psychological impact of cognitive distortions into a practical therapy for depression that combined cognitive restructuring with behavioural interventions. This revolutionised therapy in the post-war decades and has continued to ensure that CBT therapists remain focused on a patient's most pressing emotional concerns. As cognitive distortions and dysfunctional beliefs are discoverable by individuals and therapists, working together allows them to collaborate in formulating ways forward. Furthermore, Beck's commitment to empirical evaluation of theoretical models and to testing therapies in clinical trials ensured that the entire field of psychotherapy has been driven to adopting a more scientific approach.

Beck's template for CBT has been adapted and extended to an extraordinary range of conditions and his approach has influenced a number of independent research groups working on depression, all anxiety disorders, eating disorders, borderline personality disorder and psychosis. Given the growth and apparent popularity of cognitive therapy and CBT, the approaches have been closely scrutinised by the scientific community. Although some criticisms are apposite, there needs to be a greater recognition that Beck always viewed his theories as provisional only and insisted on subjecting all his ideas to rigorous testing. This philosophy extended to his many other significant research contributions, ranging from his work in suicidology to the development of the Beck Depression Inventory. No other psychiatrist or psychologist of Beck's generation has had so great an impact on psychotherapy and psychological approaches to treatment. He has been identified as one of the five most influential psychotherapists of all time and has been credited with helping to shape the face of modern psychiatry. However, for many, an abiding memory of Beck will be his generosity towards researchers and therapists and the way he encouraged, trained and inspired younger colleagues, including many from the UK.

In the 1970s, Beck asked: ‘Can a fledgling psychotherapy challenge the giants in the field – psychoanalysis and behaviour therapy?’ The answer of course is a resounding yes. Tim's work has sent out an unforgettable signal, and the introduction of CBT will rank as a milestone in the history of 20th-century medicine.