What is the name of the character who says 'The lady doth protest too much, methinks'?

The character who says “The lady doth protest too much, methinks” is Queen Gertrude.

Gertrude speaks the line in Act 3, Scene 2 of Hamlet, while watching a play-within-the-play staged by her son, Prince Hamlet. The performance depicts a queen making extravagant promises that she will never remarry after her husband’s death. Gertrude comments that the Player Queen’s declarations are too excessive to be believable.

Hamlet has arranged the performance to test Claudius, whom he suspects of murdering Hamlet’s father. The staged murder closely resembles Hamlet’s account of the real crime, and Claudius reacts so strongly that Hamlet takes his response as evidence of guilt.

In Shakespeare’s time, “protest” could mean to declare or vow, rather than simply to object. The quotation’s modern meaning—suggesting that someone’s emphatic denial seems suspicious—has broadened considerably. It is also commonly misquoted as “Methinks the lady doth protest too much.”