How to even begin to answer?

I know another version of you who became the Hero of Ferelden, and she suggested I look you up?

I've done a lot of bad things in Kirkwall so I thought I might as well use my power to be corrupt in the other direction?

The more detail he gives, the harder it is to explain, so in the end Cullen simply says, "I had the opportunity to do the right thing. So I took it."