Tim Hunt is a British biochemist associated with Cancer Research UK who shared the 2001 Nobel Prize in Physiology or Medicine with Leland Hartwell and Paul Nurse for the discovery of cyclins—proteins that oscillate in abundance through the cell cycle and act as essential regulatory subunits of cyclin-dependent kinases (CDKs). Hunt discovered cyclins while studying protein synthesis in sea urchin eggs, noticing that a particular protein was synthesized and then abruptly destroyed at each cell division. This periodic behavior turned out to be the biochemical clock controlling cell cycle entry and exit from mitosis. The cyclins he discovered (cyclin A, cyclin B) form complexes with CDK1 and CDK2, and their regulated destruction via the anaphase-promoting complex (APC/C) is essential for faithful chromosome segregation. Cyclin-CDK complexes are among the most important therapeutic targets in oncology, and Hunt's foundational discoveries underpin the development of CDK inhibitors now approved or in clinical trials for multiple cancer types.