Trait leadership is defined as integrated patterns of personal characteristics that reflect a range of individual differences and foster consistent leader effectiveness across a variety of group and organizational situations (Zaccaro, Kemp, & Bader, 2004; Zaccaro 2007). The theory of trait leadership is developed from early leadership research which focused primarily on finding a group of heritable attributes that differentiate leaders from nonleaders. Leader effectiveness refers to the amount of influence a leader has on individual or group performance, followers’ satisfaction, and overall effectiveness (Derue, Nahrgang, Wellman, & Humphrey, 2011; de Vries 2012). Many scholars have argued that leadership is unique to only a select number of individuals and that these individuals possess certain immutable traits that cannot be developed (Galton, 1869). Although this perspective has been criticized immensely over the past century, scholars still continue to study the effects of personality traits on leader effectiveness. Research has demonstrated that successful leaders differ from other people and possess certain core personality traits that significantly contribute to their success. Understanding the importance of these core personality traits that predict leader effectiveness can help organizations with their leader selection, training, and development practices (Derue et al., 2011). History of research The emergence of the concept of trait leadership can be traced back to Thomas Carlyle's "great man" theory, which stated that "The History of the World [...] was the Biography of Great Men" (Carlyle 1841, p. 17). Subsequent commentators interpreted this view to conclude that the forces of extraordinary leadership shape history (Judge, Piccolo, & Kosalka, 2009). Influenced by Carlyle, Francis Galton in Hereditary Genius (1869) took this idea further. Galton found that leadership was a unique property of extraordinary individuals and suggested that the traits that leaders possessed were immutable and could not be developed. Throughout the early 1900s, the study of leadership focused on traits. Cowley (1931) commented that the approach to the research of leadership has usually been and should always be through the study of traits (Cowley, 1931). Many theorists, influenced by Carlyle and Galton, believed that trait leadership depended on the personal qualities of the leader, however, they did not assume that leadership only resides within a select number of people (Judge, Bono, Ilies, & Gerhardt, 2002). This trait perspective of leadership was widely accepted until the late 1940s and early 1950s, when researchers began to deem personality traits insufficient in predicting leader effectiveness (Stogdill, 1948; Mann,