Final answer:
In Shakespeare's "Macbeth," the thane who informs Duncan about the Norwegian invasion and Cawdor's treason is Ross.
Step-by-step explanation:
In Shakespeare's "Macbeth," the thane who brings King Duncan news of the Norwegian invasion and reveals the thane of Cawdor's betrayal is Ross. He appears in Act 1, Scene 2, directly informing Duncan about the Norwegian advances and the disloyalty of Cawdor. It is after this revelation that Duncan decides to bestow the title of thane of Cawdor on Macbeth as a reward for his loyalty and success in battle, as expressed in the line, 'No more that thane of Cawdor shall deceive / Our bosom interest: go pronounce his present death / And with his former title greet Macbeth.' Ross is then tasked with delivering the news to Macbeth that he has been granted the title of thane of Cawdor.