[SS.I 4.0] This is a single‐case study of Mohammed Atta that utilizes Theodore Millon’s model of personality disorders to explore Atta’s transformation from a markedly shy, sensitive, and gentle person who abhorred fanaticism and violence into one of the leaders of the 9/11 terrorist attacks. First, a brief review of Atta’s life and personality is presented. This is followed by a delineation of three possible pathways that could explain his transformation. These pathways include what Millon identified as a puritanical compulsive personality, a selfless dependent personality, and a spineless denigrating personality. Because personality is complex and multifaceted, it is noted that Atta’s transformation could have been a result of some combination of these three personality dynamics. The role of personality factors, in combination with life circumstances, in expanding our understanding of the radicalization process is discussed.