Sebastian
Sebastian is the play's structural solution to the tangle created by Viola's disguise — his physical identity with Cesario allows every confused plot to resolve — and his willingness to embrace the extraordinary circumstances he finds himself in gives the comedy its final turn.
Appears In
Biography
Sebastian arrives in Illyria in Act II, Scene 1 grieving his own sister — he believes Viola drowned — and the symmetry of the two twins simultaneously mourning each other is one of the play's most quietly affecting structural jokes. He is accompanied by Antonio, the sea captain whose devotion to him is protective to the point of recklessness, and who risks arrest in Orsino's territory entirely for Sebastian's sake.
Sebastian's role in the plot is structurally simple and personally bewildering: he arrives, is immediately mistaken for Cesario by everyone he meets, is challenged to a duel by a man he has never seen (Sir Andrew), attacked by another (Sir Toby), and then swept into a betrothal by a beautiful countess who seems to know him rather better than he knows her. His response to all of this — a slightly dazed willingness to go along with whatever seems to be happening — is partly comic and partly a reasonable reaction to a situation that makes no sense.
The play asks relatively little of Sebastian's interior life, using him primarily as the mechanism by which the knots tied around Viola can be undone. But his brief soliloquy in Act IV, Scene 3 — wondering whether Olivia is mad, or he is, and settling for the pragmatic position that since she seems beautiful and clearly wants to marry him, he will — is an honest portrait of a man navigating the genuinely inexplicable with good humour and basic human willingness.
Motivation
Sebastian is motivated by grief for his sister, loyalty to Antonio, and a basic human openness to the extraordinary that allows him to accept a beautiful, wealthy, devoted stranger's proposal of marriage without requiring further explanation.
Personality
Sebastian lacks Viola's complexity because the play does not need him to carry the same emotional weight — he is the solution rather than the problem. But within his limited role he is drawn as a decent, fundamentally reasonable man who takes the extraordinary as it comes and responds with goodwill.