Answer:
Threatens to reveal Nora's indiscretions --> Krogstad
Does not trust Nora and thinks that she cannot act responsibly --> Helmer
Has been a longtime friend of Nora's --> Mrs. Linde
Acts silly but is a lot more resourceful than some think --> Nora
Step-by-step explanation:
The characters mentioned in the question belong to the play "A Doll's House" by Henrik Ibsen.
Nora: is married to Torvald Helmer. Has been treated as a toy, a doll, her whole life, constantly being told what to do, first by her father and then by her husband. Commits a crime when she forges her late father's signature to loan money from the bank where Helmer works. Accepts her role passively for a while, but then reveals herself to be strong, independent and resourceful at the end.
Helmer: Nora's husband. Sexist and ignorant. Sees himself as Nora's savior and master. Treats Nora as if she were inferior and incapable of thinking for herself.
Krogstad: works at the same bank as Helmer. Knows about Nora's crime. Threatens to reveal her secrets to her husband. Has been in love with Mrs. Linde before.
Mrs. Linde: a widow, friends with Nora for a long time. Gets back together with Krogstad after promising to help Nora.