A Great man (n.) plays the super-ego of the masses — the father-substitute for whose sake the people make their effort.
The Great man (n.) is said always to keep some infantile part; Leonardo went on playing all his life, building mechanical toys and fooling friends.
A Great man (n.) can be aped trait by trait: Lichtenberg's hero held his head askew like Alexander, drank coffee like Leibniz, and left a breeches-button undone like Cervantes.
A Great man (n.) influences his age two ways — by his personality and by his idea; and sometimes, more primitively, the personality alone does it.
A Great man (n.) is the father seen again: decisive thought, strong will, forceful deeds, self-reliance, a divine conviction of being right that may pass into ruthlessness — who else but the father was the great man of childhood?