Final answer:
Macbeth is the speaker who reacts to the ghost of Banquo during the feast in Shakespeare's play, and he is the only one who can see the apparition.
Step-by-step explanation:
The speaker in the moment when the ghost of Banquo is present at the solemn feast for the deceased Duncan, frightening Macbeth while no one else is aware of his presence, is Macbeth. This scene occurs in William Shakespeare's play Macbeth, Act 3, Scene 4, where Macbeth is the only one who can see Banquo's ghost. His reactions to the ghost cause great concern amongst the guests, as they do not see what is terrifying Macbeth.