Doctor Faustus.

I can't recall a specific reason Haust's souls is so ceveted by Lucifer. I think he just covets all souls. I could be very well making all kinds of deals with peole willing to sell their soul. There is a bit of a competition for Faust's soul in that the "good angel" works hard to counter Faust's temptations. Perhaps Lucifer wants to make an example of Faust.