Hamlet’s character changes after a visit from his deceased father. The ghost reveals the truth about his death—that it was Claudius who killed his father. It affects Hamlet’s behavior and leads to his search for vengeance. Nonetheless, there are some prompts of Hamlet being resentful from the start. The phantom’s appearance may have only intensified his feelings.
Detailed answer:
Hamlet acts bitter and incredulous from the beginning of the play. He feels resentment even towards his mother, Gertrude. In his opinion, she did not mourn his father for long and remarried quickly. The sudden death of King Hamlet is suspicious to him as well. Besides, Hamlet is hurt because Claudius has become a king. He did not have more rights than his nephew to hold power.
Thinking about whether the prince was resentful before, Hamlet seems this way from the start. After he saw his father’s ghost, he, no doubt, became more bitter and angry. The phantom revealed that Claudius killed King Hamlet with poison. It’s evident how it affected the rest of the play. The search for avenging his father didn’t make Hamlet a well-adjusted and relaxed person. The resentfulness and suspicion led to the character’s destruction. As a result, both Claudius and Hamlet died from poison.