A character who loves to spy and whose advice contradicts his behavior, the pompous and hypocritical Polonius is part of the something that "is rotten in Denmark." Given to loquaciousness, Polonius lauches into a lengthy diatribe to his son Laertes before his parting as he,ironically, advises him to be honest and forthright,
This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.
Farewell, my blessing season this in thee!(1.3.78-82)
Then, when he speaks to his daughter Ophelia, he cautions her against Hamlet and urges her to not even be near him or speak to him,
I would not, in plain terms, from this time forth
Have you so slander any moment leisure
As to give words or talk with the Lord Hamlet.
Look to't, I charge you. Come your ways. 1.3.139-143)
However, at the beginning of the next act, Scene 1, he calls his servant Reynaldo to go and spy on Laertes in France and report on his conduct.
You shall do marvellous wisely, good Reynaldo,
Before you visit him, to make inquire
Of his behaviour.(2.1.3-5)
After this, Ophelia enters to describe to her father the strange conduct of Hamlet. Instead of cautioning Ophelia again to stay away from Hamlet, Polonius suggests to her that they inform the king. He later informs Claudius and Gertrude that their son is mad. He arranges for Claudius and himself to spy on a meeting between Hamlet and Ophelia which he will arrange. Thus, with both his children, he contradicts the advice which he has given them, proving himself a hypocrite and a spy.