The speaker
The speaker is an old man, looking back on his life and reflecting on art, love, illusions, and memory. He speaks with sadness and also with wisdom, having gained a new understanding and having lost touch with many of his old dreams and fantasies.
Oisin
Oisin, the "sea-rider...led by the nose / Through three enchanted islands," is a legendary hero of Irish mythology. He is often referred to as Ireland's greatest poet and was a warrior, part of a legendary group of medieval clans called a "fianna." He has been featured in many works, including works by Yeats, who published the epic poem "The Wanderings of Oisin" in 1889. The poem is a dialogue between Oisin and St. Patrick, who originally converted Ireland to Christianity. In the poem, Oisin details his journeys into the realm of Faerie, a place often referenced in medieval literature that refers to a hidden world within our world, a place of magic and heroism and timelessness.
The fairy bride
When Yeats says "But what cared I that set him on to ride / I, starved for the bosom of his fairy bride," he is most likely referring to Niamh, the legendary fairy bride of Irish warrior-poet Oisin. Niamh, as legend has it, spotted Oisin and fell for him instantly, and invited him to come with her to Tir na t'Og, also known as the land of Faerie. There, Niamh and Oisin had children and lived forever in eternal youth.
Yeats's reference to Oisin's fairy bride could mean several things. It could be a reference to the fact that the speaker seems to long for youth, and therefore longs for the eternal youth that Niamh and the fairies are able to enjoy. It could also reference the longing for Maud Gonne, which tormented Yeats throughout his life and which was never abated; Gonne always rejected Yeats's advances. Regardless, the fairy bride represents something magical, youthful, eternal, and unattainable.
The Countess Cathleen
The Countess Cathleen is a reference to a play and a character named Cathleen, written by Yeats in 1892. The play's full title was "The Countess Cathleen and Various Legends and Lyrics." It is set in Ireland during a famine, and its seminal character, a countess, sells her soul to the devil in order to save the starving people around her. She is later redeemed and brought to heaven for her selfless motives. Yeats dedicated the play to Maud Gonne, his longtime unrequited love who dedicated her life to the cause of Irish nationalism. Yeats often lamented the violence inherent in the Irish civil war, but he clearly had some admiration for its heroic implications—Gonne, and later, Yeats's own wife were both Irish nationalists.
Referring to "The Countess Cathleen" in this poem, Yeats is referencing both his character Cathleen and his love for Gonne. Yeats laments the fact that his love's soul was destroyed by passion, fanaticism, and hate—and it seems that, in spite of his misgivings, he fell hard for the passionate sacrifices made by his love. His love became a "dream," a false illusion that captured and enchanted him but that only now is dissolving into the nothingness it really always was.
The Fool and the Blind Man
"The Fool" and "The Blind Man" are both references to the myth of Cuchulain, discussed below.
Cuchulain
Cuchulain was a hero of Irish mythology. He was a legendary warrior, and in some iterations was said to be the child of gods, endowed with godlike power.
