Final answer:
Claudius is the brother who poisoned Hamlet's father, setting off the central conflict in the play. The character of the Ghost spawns multiple interpretations and symbolizes larger themes such as betrayal, revenge, Catholic oppression, and the supernatural.
Step-by-step explanation:
The Ghost is indeed the spirit of Hamlet's father, who was poisoned by his own brother, Claudius. The presence of the Ghost in Hamlet permeates the play with themes of betrayal, revenge, and the questioning of reality.
Opinions among the characters about the Ghost's authenticity vary: while Horatio fears it may be a demon, and Gertrude and Claudius dismiss it as a product of Hamlet's madness, Hamlet himself grapples with its true nature. The Ghost not only propels the action by revealing the truth about Claudius's regicide but also offers a rich analysis of the period's views on spirituality, sanity, and the supernatural.
Literary analysis of the Ghost might consider its role as a symbol of Catholic oppression during Shakespeare's time, as well as Hamlet's potential unreliability as a narrator.
The complexity of the Ghost's role is further highlighted by differing literary critiques, such as Harold Bloom's assertion of its authenticity and T.S. Eliot's analysis of Hamlet's emotions and the thematic issues within the play.