"Leave her...to those thorns that in her bosom...prick and sting her" refers to which Shakespearean character?

In William Shakespeare's play "Hamlet", the ghost of Hamlet's father returns (Act 1, scene 5) and urges Hamlet not to seek vengeance against his mother, Queen Gertrude. Hamlet is told to "leave her to heaven, and to those thorns that in her bosom lodge to prick and sting her". Hamlet is directly instructed not to punish the queen, his mom and wife to the late King Hamlet.

In the play, Gertrude is the Queen of Denmark and her relationship with Hamlet is somewhat turbulent. He has resented her marrying her husband's brother Claudius, especially after Claudius murdered the king (young Hamlet's father, King Hamlet).

Gertrude reveals no guilt in her marriage to Claudius, and Hamlet can only show real signs of jealousy towards his uncle. According to Hamlet, she, his mother, scarcely mourned her husband's death before marrying his brother, Claudius. Later, the ghost makes another appearance and implores Hamlet to comfort her. It is implied that she has some reason to be spiritually conflicted.