“Great necessities call forth great leaders.”
This seems to first appear in Why Leaders Can't Lead : The Unconscious Conspiracy Continues (1989) by Warren G. Bennis, p. 159, where it is cited as being from a letter to Thomas Jefferson, but it might be a misquote of "Great necessities call out great virtues" stated in a letter to her son John Quincy Adams (19 January 1780)
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Abigail Adams 40
2nd First Lady of the United States (1797–1801) 1744–1818Related quotes
On Winston Churchill http://www.amazon.com/review/R7UQOFFBBBUNN/

“Great leaders are formed only by taking on great challenges.”
Source: 2010s, Winter is Coming (2015), p. 190

Video commentary featured on website of the Chicago Public Education Fund http://www.cpef.org/nm_video.htm#

As quoted in Three Faces of Fascism: Action Française, Italian Fascism, National Socialism, Ernst Nolte, New York: NY, Holt, Rinehart and Winston (1966) p. 156. Opera Omnia di Benito Mussolini, V, p. 121
Undated

Source: Start with Why: How Great Leaders Inspire Everyone to Take Action

“Ya know, Hitler was a great leader, too.”
On Michigan Wolverines head coach Rich Rodriguez, as attributed by Dick Weiss, "Lou Holtz sorry for Hitler line" http://www.nydailynews.com/sports/college/2008/10/18/2008-10-18_lou_holtz_sorry_for_hitler_line.html#ixzz0RfdSeZwT, New York Daily News.com, 17 October 2008
Attributed

Speech before the 2004 Republican National Convention in New York. August 30, 2004. http://news.bbc.co.uk/2/hi/americas/3613480.stm

“Great times call for great men.”
Preface
The Good Soldier Švejk (1921)
Context: Great times call for great men. There are unknown heroes who are modest, with none of the historical glamour of a Napoleon. If you analysed their character you would find that it eclipsed even the glory of Alexander the Great. Today you can meet in the streets of Prague a shabbily dressed man who is not even himself aware of his significance in the history of the great new era. He goes modestly on his way, without bothering anyone. Nor is he bothered by journalists asking for an interview. If you asked him his name he would answer you simply and unassumingly: 'I am Švejk….