Final answer:
The lines mention Young Fortinbras; however, they are from Shakespeare's 'Hamlet', not 'Macbeth'. Fortinbras is not a character in 'Macbeth' but is indeed the person referenced in the given lines.
Step-by-step explanation:
In the lines ". . . Young Fortinbras,/ Holding a weak supposal of our worth/ Or thinking by our late brother's death/ Our state to be disjoint and out of frame . . .", the person mentioned is Fortinbras. These lines do not actually come from Shakespeare's "Macbeth" but from "Hamlet", another one of Shakespeare's well-known plays. In "Macbeth", common themes revolve around ambition, fate, deception, and guilt, as evident in the interactions between characters such as Macbeth, Banquo, and Lady Macbeth. However, Fortinbras is a character exclusive to "Hamlet", where he is the Prince of Norway and represents a parallel to Hamlet's own situation, while also posing a potential threat to the kingdom of Denmark.