Carlyle moved towards his later thinking during the 1840s, leading to a break with many old friends and allies, such as Mill and, to a lesser extent, Emerson.
His belief in the importance of heroic leadership found form in the book On Heroes, Hero-Worship, and The Heroic in History, in which he was seen to compare a wide range of different types of heroes, including Odin, Muhammad, Oliver Cromwell, Napoleon, William Shakespeare, Dante, Samuel Johnson, Jean-Jacques Rousseau, Robert Burns, John Knox, and Martin Luther.
These lectures of Carlyle's are regarded as an early and powerful formulation of the Great Man theory of historical development.

For Carlyle, the hero was somewhat similar to Aristotle's "magnanimous" man – a person who flourished in the fullest sense.
However, for Carlyle, unlike Aristotle, the world was filled with contradictions with which the hero had to deal.
All heroes will be flawed.
Their heroism lay in their creative energy in the face of these difficulties, not in their moral perfection.
To sneer at such a person for their failings is the philosophy of those who seek comfort in the conventional.
Carlyle called this "valetism", from the expression "no man is a hero to his valet."
Carlyle moved towards his later thinking during the 1840s, leading to a break with many old friends and allies, such as Mill and, to a lesser extent, Emerson. His belief in the importance of heroic leadership found form in the book On Heroes, Hero-Worship, and The Heroic in History, in which he was seen to compare a wide range of different types of heroes, including Odin, Muhammad, Oliver Cromwell, Napoleon, William Shakespeare, Dante, Samuel Johnson, Jean-Jacques Rousseau, Robert Burns, John Knox, and Martin Luther. These lectures of Carlyle's are regarded as an early and powerful formulation of the Great Man theory of historical development.
For Carlyle, the hero was somewhat similar to Aristotle's "magnanimous" man – a person who flourished in the fullest sense. However, for Carlyle, unlike Aristotle, the world was filled with contradictions with which the hero had to deal. All heroes will be flawed. Their heroism lay in their creative energy in the face of these difficulties, not in their moral perfection. To sneer at such a person for their failings is the philosophy of those who seek comfort in the conventional. Carlyle called this "valetism", from the expression "no man is a hero to his valet."
Thomas Carlyle