What do we know about krogstad and his past? How does tolvarld feel about krogstad? How does this affect Nora?

We know that Krogstad (along with Nora) has been committing forgery. And in his own words, “For the last eighteen months I’ve gone straight; all the time it’s been hard going. I was content to work my way up, step by step.” This is not explained, but it does allude that he has been up to something.