The brother of the former king who committed murder in order to win the crown and marry the queen, Claudius contrasts sharply with most of the other major male characters. While Hamlet, Laertes, and Fortinbras are obsessed with problems of justice, revenge, and moral balance, Claudius only looks out for Claudius. He is clever, conniving, and manipulative, and his main goal is to maintain his own power.
Claudius’s primary skill is his ability to manipulate others through the clever use of language. His choice of means to murder the previous king is therefore significant: Claudius pours poison into the king’s ear. Metaphorically, his ability to manipulate people with language is also a sort of “pouring poison into their ears.” Claudius is not interested in what harm his words might cause, as long as he gets the result he wants.
Claudius’s primary obsession is his own safety and advancement, not the health of Denmark. When reacting to Polonius’s death, he notes twice that if he had been in the room, Hamlet would have killed him: once to Gertrude and once to Laertes. The fact that Gertrude was present when Polonius died or that Laertes is grieving the murder of his father never occur to Claudius.
Ultimately, Claudius’s scheming is his undoing. While Laertes agrees to the plot to use the duel to kill Hamlet, Laertes wants to do it only with a sharpened sword. This method gives him a secret advantage over Hamlet, but Laertes must still display better swordsmanship in order to kill Hamlet, indicating that the playing field, while not entirely level, is still somewhat honorable. It is Claudius’s idea to poison the blade and to offer Hamlet the poisoned cup of wine that ends up killing both Claudius and Gertrude.