Not only is Hamlet deceptive, but so are the other characters. Horatio, Claudius, Polonius, Ophelia, Rosencrantz and Guildenstern, Fortinbras, and Laertes are all simultaneously manipulating each other as well as Hamlet.
Deception is evident in the opening act of the play. Hamlet portrays himself as someone who detests lies, corruption, and deceit. He explains that his grief is real and not simply a facade to feign his madness. He is adamant that his feelings are genuine.
Throughout the entire play, Hamlet is manipulative, wise with his words and actions, and convinces everyone he is insane. He does these things because he is obviously grief-stricken with the news of his father's murder and is angry at the person who did it, his uncle and his father’s murderer. He is also confused and hurt that his mother would marry his uncle, especially in such a short time after King Hamlet's death. Not to mention he feels it is incestuous that his uncle is now his step father. He refers to his mother as the "good mother," or step mother. He lies about his mental state to refrain from arousing suspicion and to create a distraction. While Hamlet gathers evidence against Claudius, he reveals to Horatio his plan to feign insanity:
Here, as before, never, so help you mercy,
How strange or odd soe'er I bear myself,
As I, perchance, hereafter shall think meet
To put an antic disposition on,
That you, at such times seeing me,...