Willi Sauerbrei is a senior statistician and professor in medical biometry. Since 1983, he has worked as an academic biostatistician with a main interest in various issues of model building and in cancer research. For 16 years, he was the head of a Clinical Trials Unit. With Patrick Royston, he has developed the multivariable fractional polynomial approach (MFP) and extensions of it. Methodological topics of interest include variable and function selection, model stability, treatment covariate interactions, meta-analysis, reporting of research findings, and high-dimensional data. He is the initiator and chair of the STRATOS (STRengthening Analytical Thinking for Observational Studies) initiative.