Final answer:
King Hamlet's ghost is speaking, revealing the truth about his death and how it was Claudius who killed him. This revelation is significant as it drives the plot forward and introduces themes of betrayal, revenge, and the supernatural.
Step-by-step explanation:
The speaker in the quoted passage is a. King Hamlet's ghost, revealing the truth about his death. This is significant because it sets the stage for the entire plot of the play, as it triggers Hamlet's quest for revenge against his Uncle Claudius, who is now king. The ghost's revelation that he was murdered by the very person who has taken his place on the throne represents the betrayal and the moral corruption within the royal family of Denmark. It also adds a supernatural element to the play that raises questions about the reliability of the ghost and whether it is a true spirit, a demon, or a product of Hamlet's own imagination.