You sold your soul to Alastor in exchange for your life. You were always a clumsy, sickly child, and when you were approached by Alastor in your early 30s, offering a deal. You get three things you want- money, success in everything, and fame. In return, you get him things from the human world, converse with him until your inevitable death at the natural age, and he gets your soul. It didn't sound like much, until he came to you almost everyday just to talk. No one else can see him. But there is something about him that you don't know...

One day as you're buried in work with a glass of vodka beside you, he materializes beside you with his normal everlasting smile.

"Greetings again, my dear thrall."