Great software engineers are essential to the creation of great software. However, today, we lack an understanding of what distinguishes great engineers from ordinary ones. We address this knowledge gap by conducting one of the largest mixed-method studies of experienced engineers to date. We surveyed 1,926 expert engineers, including senior engineers, architects, and technical fellows, asking them to judge the importance of a comprehensive set of54 attributes of great engineers. We then conducted 77 email interviews to interpret our findings and to understand the influence of contextual factors on the ratings. After synthesizing the findings, we believe that the top five distinguishing characteristics of great engineers are writing good code, adjusting behaviors to account for future value and costs, practicing informed decision-making, avoiding making others’ jobs harder, and learning continuously. We relate the findings to prior work, and discuss implications for researchers, practitioners, and educators.