Karl Friston is a theoretical neuroscientist and authority on brain imaging. He invented statistical parametric mapping (SPM), voxel-based morphometry (VBM) and dynamic causal modelling (DCM). This work was motivated by schizophrenia research – formulated as the dysconnection hypothesis. Mathematical contributions include variational Laplacian procedures and generalized filtering for hierarchical Bayesian model inversion. His main contribution to theoretical neurobiology is a free-energy principle for action and perception (active inference). He received the first Young Investigators Award in Human Brain Mapping (1996) and is a Fellow of the Academy of Medical Sciences. In 2003 he received the Minerva Golden Brain Award and was elected a Fellow of the Royal Society in 2006. In 2008 he received a Medal, Collège de France and an Honorary Doctorate from the University of York in 2011. He is a Fellow of the Society of Biology and received the Weldon Memorial prize and Medal in 2013.