It is unknown how the Lord of the Nine Hells came to be, or when he came into existence, though it is known that he has existed at least since the Beginning, if not before then.
The Lord of the Nine Hells commands absolute authority and power throughout The Nine Hells, though his primary residence is on the Ninth Layer known as Nessus, and ultimately owns all souls that reside within its layers. As such The Lord of the Nine Hells does not need to make contracts, but enjoys
doing so when it pleases him. He reportedly favours those who seek dark
power and are easily seduced by the promise of it.
The true name, even a shortened version of it, of the Lord of the Nine Hells is said to be known only by him. Some think that perhaps Archdevil Valkyre Xephira, also knows it, but if this is the case she has never been known to use it.
Exactly what the Lord of the Nine Hells' relationship with Lady Valkyre Xephira is also unclear, with some accounts stating that she is his wife, and others that she is his slave. Regardless, it is generally understood that she is the mother of his children: Crucius Xephira, Au'ra Xephira, Darke Xephira, Elvira Xephira, Mortius Xephira, and Elistra Xephira.
His appearance is also disputed, and it is said that his true form is too terrible to behold and beyond mortal comprehension. Indeed tieflings of his bloodline (Tiefling (Lord of the Nine Hells)) have no known unifying features that might help in this matter.
With the GM's permission, The Lord of the Nine Hells may be chosen as a Warlock patron as a Fiend or Great Old One. Regardless, the price for such patronage is invariably one's soul and perhaps more besides.