It is none other than Macbeth himself who kills the younger Siward in battle at Dunsinane in William Shakespeare's tragic Macbeth. Malcolm orders Siward to lead the attack with his son at his side.
"You, worthy uncle,
Shall, with my cousin, your right-noble son,
Lead our first battle" (Act V, Scene 6, Lines 2-4)
On the battlefield, Young Siward comes upon Macbeth and asks his name. Replies Macbeth, "Thou'lt be afraid to here it." When Young Siward declares that he fears no one, Macbeth repeats that fear will overtake his foe, and then identifies himself. The brash Young Siward takes up the challenge.
"Thou liest, abhorred tyrant; with my sword
I'll prove the lie thou speak'st. (Act V, Scene 7, Lines 10-11)
They fight, and Macbeth kills the young man.
In Act V Scene 7, Macbeth himself kills young siward. When Macbeth identifies himself to Siward. he anticipates fear. He is more than a little surprised when he encounters vehement loathing instead; Line 4:
YOUNG SIWARD: What is thy name? MACBETH: Thou'lt be afraid to hear it.
No, though thou call'st thyself a hotter name Than any in hell.
They argue alittle bit about whether Macbeth should be hated or feared. They then fight and young Siward if killed. Macbeth then gloats the Witches prophecy that none born of woman shall kill him in Lines 11-13:
MACBETH Thou art born of woman. But swords I smile at, weapons I laugh to scorn, Brandished by man that's of woman born.
Macbeth kills young Siward as he virtually tests the witches' prediction that "no man of woman born" can defeat him. The fact that this is an unproven young soldier and Macbeth is a war hero doesn't even phase Macbeth. This is a great indicator of the deluded mind with which he was now seeing the world around him.