Final answer:
In Shakespeare's 'Macbeth', Lady Macbeth is the character who advises Macbeth to 'look like the innocent flower, But be the serpent under't' as part of her plan to seize the throne.
Step-by-step explanation:
In William Shakespeare's Macbeth, it is Lady Macbeth who advises Macbeth to appear innocent like a flower but be deceitful like a serpent. This advice is given as part of her manipulative encouragement to Macbeth to commit regicide and seize the throne. She articulates this when she says, "Your face, my thane, is as a book where men May read strange matters. To beguile the time, Look like the time; bear welcome in your eye, Your hand, your tongue: look like the innocent flower, But be the serpent under't." This statement encapsulates her deceitful nature and cunning plan for obtaining power.