What important roles do Banquo have in the play Macbeth?

You can proceed on the basis of the following
leads:

a) Banquo accompanies Macbeth to victory in the
battle against the rebels and traitors;

b) Banquo
accompanies Macbeth on their way back to the king when the witches appear on the heath.
The witches prophesy about Macbeth's as well as Banquo's future. Banquo notices
Macbeth's awkward responses to the witches'
proclamations.

c) Banquo accompanies Macbeth to appear
before King Duncan who admires both of them, but Macbeth is more profusely rewarded and
acknowledged than Banquo;

d) Banquo accompanies Duncan
during his visit to Macbeth's castle;

e) After the
discovery of Duncan's murder, Banquo mouths pious resolution to 'stand in the hands of
God', but does nothing towards the redressal of the foul crime and injustice
committed;

f) While Macbeth is haunted by the witches'
prophetic soliciting, Banquo is also tempted by the prophecy that his issues would be
the kings of Scotland. He doesn't confront the usurper king, but rather
compromises;

g) Banquo is killed by Macbeth just before the
coronation banquet, but the ghost of Banquo, a hallucinatory product of Macbeth's guilt
and fear, appears at the Banquet to force Macbeth reveal his crime, and to lead him to
the witches for the final round of doom;

h) Banquo is a
foil to Macbeth, a sort of alter image. He is deliberately made an incomplete
characterization.

i) Banquo has been very curiously used by
Shakespeare as a part of the play's elaborate supernatural machinery. Banquo's ghost
proves that dead Banquo is more potent a threat for Macbeth than living
Banquo.