By Jonathan Dunnemann
The poem was written in 1875 and first published in 1888 in Henley’s Book of Verses, where it was the fourth in a series of poems entitled Life and Death (Echoes). It originally bore no title. Early printings contained only the dedication To R. T. H. B.—a reference to Robert Thomas Hamilton Bruce (1846–1899), a successful Scottish flour merchant and baker who was also a literary patron. The familiar title “Invictus” (Latin for “unconquered”) was added by Arthur Quiller-Couch when he included the poem in The Oxford Book Of English Verse (1900).
William James said…
For morality life is a war, and the service of the highest is a sort of cosmic patriotism which also calls for volunteers. Even a sick man, unable to be militant outwardly, can carry on … [in] moral warefare. He can willfully turn his attention away from his indifference to his present drawbacks and immerse himself in whatever objective interests still remain accessible. He can follow public news, and sympathize with other people’s affairs. He can cultivate cheerful manners, and be silent about his miseries. He can contemplate whatever ideal aspects of existence his philosophy is able to present to him, and practice whatever duties, such as patience, resignation, trust, his ethical system requires. Such a man lives on his loftiest, largest plane. He is a high-hearted freeman and no pining slave.
 From Wikipedia, the free encyclopedia. (http://en.wikipedia.org/wiki/Invictus)
 Assagiolo, M.D., R. (N/A). The Training of the Will (http://www.synthesiscenter.org/articles/0117.pdf)
James, W., (2004). The Varieties of Religious Experience – A Study in Human Nature. With Introduction and Notes by Wayne Proudfoot Barnes & Noble Classics. New York.