Nearly all workers have a supervisor or 'boss'. Yet there is almost no published research by economists into how bosses affect the quality of employees' lives. This study offers some of the first formal evidence. First, it is shown that a boss's technical competence is the single strongest predictor of a worker's well-being. Second, we examine equivalent instrumental-variable results. Third, we demonstrate longitudinally that even if a worker stays in the same job and workplace then a newly competent supervisor greatly improves the worker's well-being. Finally, we discuss analytical possibilities, and consider necessary future research.