Claudius is the new King of Denmark, and Hamlet's uncle. He is not a nice guy – he poisoned Hamlet's father, usurped the throne, and then married Hamlet's mother. Now that he knows Hamlet is onto him, he is searching for a way to kill him (this is why he sends Hamlet to England). He is a minor character in this play. He uses the guileless Ros and Guil to keep tabs on Hamlet, and gets the two of them to do his bidding. It does seem that he is disturbed by Hamlet's play, which depicts the way that he usurped the throne, but it's not clear if this is remorse or fear that Hamlet will ruin his plan.