Banquo receives a prophecy from the witches, alonside Macbeth, that even though he won't be king, he will be father to kings. Banquo is a virtuous, brave man who has fought alongside Macbeth to defend Scotland and King Duncan.
Banquo does not have any intention of overthrowing Macbeth. Once Macbeth becomes king, he becomes totally paranoid and sends killers to take out Banquo and his son Fleance.
Banquo does not intend to overthrow Macbeth, he does not even get a chance to stand and watch Macbeth govern as King. He is murdered shortly after Macbeth is crowned.
"Unlike Macbeth, who appears to be fascinated by the weird sisters, Banquo expresses doubts about the witches and their prophesies. He comments to Macbeth, for example, that ''oftentimes, to win us to our harm, / The instruments of darkness tell us truths, / Win us with honest trifles, to betray [us]" (I.iii.123-25).