In brief...
The brave, noble general whose children, according to the witches' prophecy, will inherit the Scottish throne. Like Macbeth, Banquo thinks ambitious thoughts, but he does not translate those thoughts into action. In a sense, Banquo's character stands as a rebuke to Macbeth, since he represents the path Macbeth chose not to take: a path in which ambition need not lead to betrayal and murder. Appropriately, then, it is Banquo's ghost—and not Duncan's—that haunts Macbeth. In addition to embodying Macbeth's guilt for killing Banquo, the ghost also reminds Macbeth that he did not emulate Banquo's reaction to the witches' prophecy.
In Shakespeare's play, Banquo is depicted as Macbeth's rival; the role of fellow plotter passed to Lady Macbeth. Like Macbeth, Banquo is open to human yearnings and desires. He is, for example, just as keen to hear what the Witches have in store for him in Act I, Scene 3. He is kept from sleep by his dreams of the Witches (Act II, Scene 1). And in his soliloquy at the start of Act III, Scene 1 — "Thou hast it now . . . " — there is more than a hint of resentment and, possibly, of the same naked ambition that leads Macbeth astray. Nevertheless, Banquo is a sympathetic figure for several reasons. First, he is ignorant of what the audience knows concerning the murder of the king and of his own impending doom. Second, he is a father whose relationship with his son is clearly an affectionate one.
The Real Banquo
In Holinshed's Chronicles, the historical work on which Shakespeare based his play, the real Banquo is depicted as a conniver who took part in the plot to assassinate King Duncan. Why did Shakespeare portray Banquo as one of Macbeth's innocent victims? Perhaps because James I, the King of England when the play debuted, was a descendant of Banquo. It would not do to suggest that His Royal Majesty's ancestor was a murderer.
This is super short i know but its not likely that Banquo will come up for you as an exam question the only way that he will come up is that of a comparison question. This is where you would compare Macbeth and Banquo together as they are the exact opposite of each other