His "best friend" and fellow soldier before he ascended to kingship, Banquo. One of the prophecies mentions Banquo's predecessors being Kings, as in his son, grandson, great-grandson etc. So Macbeth orders for him and his son to be killed so that he may never produce a child that threatens Macbeth's throne. However Banquo's son survives, and Banquo does not.
