A Lord in the D-Verse is the term for both a mantle of responsibility and the person who wears it.
Origin and purpose Edit
Lords were created some time after the Pantheon, with the intent that they fill the gaps that exist between the Deities' respective domains. While the Deities' domains are considered more overarching or permanent, the Lords' domains are somewhat more mutable and nebulous, meaning that there are many more Lords than Deities and a varying number of them as well.
A Lord is differentiated from other mortals by virtue of the mantle they wear. It provides them complete power over their domain, excepting the oversight of the Deities, but also ties them inextricably to the state of that domain - a weakness to which Deities are not subject.
The mantle of a Lord also provides them with agelessness - along with all the powers of their domain - as long as they wear it, and has a noticeable residual effect as well: any Lord who gives up or passes on their mantle begins their new life at the same age as when they took the mantle the first time, but lives somewhere between half again and twice their original remaining lifespan, where applicable.
Lords function in something approximating a hierarchy, beginning with domains directly derived from or otherwise linked to a Deity's domain and continuing down through further derivations. Though the Lords of a derived domain may be more powerful - the Lord of Nightmares being more powerful than the Lord of Dreams, for example - they are still subject to the edicts of the domains (and the Lords thereof) from which theirs are derived.