One reason why Macbeth is respected and well-liked by King Duncan is that Macbeth had proven his prowess in battle. He was very instrumental in helping King Duncan defeat a rebel, Macdonwald, who had Irish spies. The sargeant who reports Macbeth's heroic deeds to the audience during the play does so in glowing terms:
"For brave Macbeth—well he deserves that name—
Disdaining fortune, with his brandish'd steel,
Which smoked with bloody execution," (I.ii.)
Through this description, Shakespeare portrays Macbeth as both a warrior and a hero. Moreover, Macbeth also defeated another traitor to the crown, the Thane of Cawdor who had been allied with the Norwegians, who were attacking Scotland at the start of the play. Macbeth's powerful defeat of the thane of Cawdor leads to an all-around victory for the Scots against the Norwegian king.