I will post a CS for Arik soon. Mika knows about him, but I'll give brief explanation of who he is.

He's a demon. He's god knows how many hundreds of years old, and doesn't remember much about being a human. He made a deal to save a girl, and ended up cast into hell (much like Dean could have been) where he was made a demon. He answers to Lucifer, against his will for now. When AnnaBeth was a child, he was obsessed with her, and watched her, wherever she went. Now that she's an adult, he's in love with her, and up until a mysterious stranger confirmed the baby as a Winchester, it was thought that AnnaBeth's baby was actually Arik's, which scared Dean.