First described by Weber in 1947, and later by Burns in 1978, transactional leaders were one of the two main categories of leaders documented; the other being transformational leaders. Transactional leaders are characterized by their ability to seize opportunities through bargaining, or the exchange of favors.
Transactional leaders are willing to work within existing systems and negotiate to attain the goals of the organization. They are leaders that tend to think "inside the box" to solve problems. This is at the opposite side of the spectrum from the transformational leader, who is comfortable seeking solutions that are innovative and without constraints.
The leadership models of both Weber and Burns theorized that leaders would actually fall along a continuum of leadership qualities, which included transformational leaders at one end of the spectrum and transactional leaders at the other.
Burns was also careful to distinguish between moral leaders and amoral leaders.