Who is seyward in the play Macbeth?

Young Siward is the son of Siward, Earl of Northumberland, and fights on the side of Malcolm in his rebellion against Macbeth. He is described as "manly" (V.vii.23) and "gentle" (V.viii.10), and proves himself to be "bloody and bold" (V.vii.24) in battle. He is killed in combat by Macbeth, and his death is bitterly mourned by Malcolm and Macduff.