Quote 1
KROGSTAD: "My sons are growing up; for their sake I must try and win back as much respect as I can in the town. This post in the Bank was like the first step up for me—and now your husband is going to kick me downstairs again into the mud." (1.358)
Regaining his good name is Krogstad's major motivating force throughout the entire play.
Quote 2
KROGSTAD: "I will tell you. I want to rehabilitate myself, Mrs. Helmer; I want to get on; and in that your husband must help me." (2.283)
It's ironic that Krogstad wants to fix his seedy reputation by blackmailing someone.
Quote 3
KROGSTAD: "Or perhaps that you have some expedient for raising the money soon?
NORA: "No expedient that I mean to make use of." (2.259-2.260)
Nora is referring to her decision not to borrow money from the lovesick Dr. Rank. Why doesn't she want to borrow it from him? Does she not want to manipulate him? Or does she feel like she'd be selling herself in some way?
Quote 4
KROGSTAD: "I shall only preserve it—keep it in my possession. No one who is not concerned in the matter shall have the slightest hint of it." (2.263)
Rather than blackmailing the Helmers for money, Krogstad is seeking to regain his reputation... showing what he truly values as a character.
Quote 5
KROGSTAD: "How will you be able to prevent it? Am I to understand that you can pay the balance that is owing?" (2.257)
Nora's debt gives Krogstad power.