Simple logic dictates that some suicide terrorists are more significant than others. However, major questions still remain about the motives and psychology of 9/11 ringleader Mohamed Atta, arguably the most significant suicide terrorist in human history. This article constructs a psychological autopsy of Atta in order to provide a much more complete explanation of his behavior. First, it suggests that accounts which solely attribute Atta’s actions to religious and political ideology appear severely incomplete. It then reviews evidence that Atta may have been clinically suicidal, and that his struggles with social isolation, depression, hopelessness, guilt, and shame were extraordinarily similar to the struggles of those who commit conventional suicide. Finally, it considers how Atta’s ideology may have interacted with his suicidal tendencies to produce his final act of murder-suicide on September 11, 2011.