Karl Friston is a theoretical neurobiologist and Professor of Neuroscience at University College London. He is also an honorary consultant at UCL’s Queen Square Institute of Neurology and is a fellow of both the Academy of Medical Sciences and the Royal Society. He is also the most cited neuroscientist in the world. As an undergraduate at Cambridge University he studied natural sciences, with a specialism in physics and psychology, and went on to train as a psychiatrist. He first rose to prominence after inviting multiple techniques for analysing brain imaging data and later turned his attention to developing a unified theory of the brain; the Free Energy Principle.