The scientific career of eminent experimentalist and psychological tester James McKeen Cattell (1860–1944) began at the Johns Hopkins University during the year (1882–1883) he held the university’s Fellowship in Philosophy. This article opens by sketching the scope of Cattell’s lifetime achievement and then briefly reviews the historical attention that his life and career has attracted during the past few decades. It then outlines the origins and evolution of Cattell’s “scientific ideology,” traces the course of events that led to his fellowship, reviews his earliest studies at Johns Hopkins, and analyzes in some detail his initial laboratory successes. These laid the groundwork for his later distinguished work as a psychological experimentalist, both in Europe and America. It concludes, however, that even as Cattell’s early experimental achievements impressed others, the personal arrogance he exhibited during his year in Baltimore served to alienate him from his colleagues and teachers. Over the long run, this arrogance and his often-antagonistic approach to others continued to color (and even shape) his otherwise distinguished more than 50-year scientific career.