Stephen Dedalus is James Joyce's literary alter ego, appearing as the protagonist and antihero of his first, semi-autobiographic novel of artistic existence, A Portrait of the Artist as a Young Man (1916), and as a major character in his modernist novel Ulysses (1922). Stephen mirrors many facets of Joyce's own life and personality. Joyce was a talented singer, for example, and in Ulysses Leopold Bloom notes the excellence of Stephen's tenor voice after hearing him sing Johannes Jeep's song "Von der Sirenen Listigkeit".

In Stephen Hero, an early version of A Portrait, Stephen's surname is spelled "Daedalus," a more obvious allusion to the mythological figure Daedalus, a brilliant artificer who constructed a pair of wings for himself and his son Icarus as a means of escaping the island of Crete, where they had been imprisoned by King Minos. Buck Mulligan makes reference to Stephen's mythic namesake in Ulysses, telling him, "Your absurd name, an ancient Greek!" His surname also suggests his desire to "fly" above the constraints of religion, nationality, and politics in his development as an artist. Daedalus had been contracted by King Minos to build the Labyrinth in which he would imprison his wife's son the Minotaur. Stephen's surname may also reflect the labyrinthine quality of his developmental journey in A Portrait of the Artist as a Young Man. Stephen's first name recalls the first Christian martyr. The theme of martyrdom runs throughout the novel.

Once upon a time and a very good time it was there was a moocow coming down along the road and this moocow that was coming down along the road met a nicens little boy named baby tuckoo ...

His father told him that story: his father looked at him through a glass: he had a hairy face.

He was baby tuckoo. The moocow came down the road where Betty Byrne lived: she sold lemon platt.

— James Joyce, opening to A Portrait of the Artist as a Young Man

The childhood of Stephen Dedalus is recounted using vocabulary that changes as he grows, in a voice not his own but sensitive to his feelings. The reader experiences Stephen's fears and bewilderment as he comes to terms with the world in a series of disjointed episodes. Stephen attends the Jesuit-run Clongowes Wood College, where the apprehensive, intellectually gifted boy suffers the ridicule of his classmates while he learns the schoolboy codes of behaviour. While he cannot yet grasp their significance, at a Christmas dinner he is witness to the social, political and religious tensions in Ireland involving Charles Stewart Parnell, which drive wedges between members of his family, leaving Stephen with doubts over which social institutions he can place his faith in. Back at Clongowes, word spreads that a number of older boys have been caught "smugging" (the term refers to the secret homosexual horseplay that five students were caught at); discipline is tightened, and the Jesuits increase use of corporal punishment. Stephen is strapped when one of his instructors believes he has broken his glasses to avoid studying. Prodded by his classmates, Stephen works up the courage to complain to the rector, Father Conmee, who assures him there will be no such recurrence, leaving Stephen with a sense of triumph.

Stephen's father gets into debt and the family leaves its pleasant suburban home to live in Dublin. Stephen realises that he will not return to Clongowes. However, thanks to a scholarship obtained for him by Father Conmee, Stephen is able to attend Belvedere College, where he excels academically and becomes a class leader. Stephen squanders a large cash prize from school, and begins to see prostitutes, as distance grows between him and his drunken father.