What does Krogstad's first appearance on stage and in Dr Rank's remarks about him indicates that the bank clerk is a menace?

Krogstad's first appearance on stage and Dr. Rank's remarks suggest that Krogstad is seen as a morally questionable character. Krogstad is described by Dr. Rank as someone with a shady reputation and a past involving forgery. This sets the tone for Krogstad's role as a potential threat or antagonist in the play.