The supreme quality for leadership is unquestionably integrity. Without it, no real success is possible, no matter whether it is on a section gang, a football field, in an army, or in an office. If a man’s associates find him guilty of phoniness, if they find that he lacks forthright integrity, he will fail. His teachings and actions must square with each other. The first great need, therefore, is integrity and high purpose.

Dwight David Eisenhower (1890-1969) American general, US President (1953-61)

(Attributed)
    (Source)

The earliest citation found for this quote is in J. A. Cheley, Stories for Talks with Boys and Girls (1958). More discussion here.