At the beginning of the play, specifically Act 1, sc. 2, Macbeth is shown to be a brave soldier, valiant and successful in battle. The Captain, when talking to Malcolm and Duncan about the battle from which he's just come, describes Macbeth as, "For brave Macbeth (well he deserves that name),..." and tells about how courageously Macbeth fought and defeated the foe. He also tells Malcolm and Duncan what Macbeth did to his opponent, Macdonwald, "...he unseamed him from the nave to the chops / And fixed his head upon our battlements," which indicates to the reader that Macbeth is, as well as a good soldier, a blood-thirsty soldier who takes no pity on those he defeats in battle.
At the end of this scene, as a reward for his success on the battlefield, Duncan says that he is going to confer the title of Thane of Cawdor upon Macbeth since the former Thane of Cawdor has just been defeated in battle and proved a traitor. This indicates that Macbeth is viewed, also, as a loyal subject to the king, ironically, since the king is giving the title to Macbeth.