Fleance
Fleance is a minor character whose dramatic function is entirely symbolic: he is the future that Macbeth cannot erase. His escape preserves the witches' prophecy and ensures that Macbeth's violence cannot secure what it seizes.
Appears In
Biography
Fleance is Banquo's son, a boy whose survival of the murderers sent to kill him and his father is one of the play's pivotal moments. The witches have prophesied that Banquo's descendants shall be kings, and Fleance's escape means that prophecy remains alive.
He appears only briefly — in Act II at his father's side, and in Act III as the one who escapes while Banquo is killed. After that he vanishes from the play entirely. His importance is structural rather than characterological.
His survival is the source of Macbeth's residual terror even at the height of his power: the line of Banquo extends into a future he cannot control.
Motivation
Fleance's only motivation is survival — he flees because his father tells him to. He is not yet old enough to have the kind of agency the play rewards or punishes.
Personality
Fleance is too lightly drawn to have a psychology. His youth and his escape are the entirety of his dramatic meaning — the seed of a future the play cannot yet show us.