Larloch
Larloch is a infamous and massively powerful Lich in the Forgotten Realms campaign setting. While he isn't as visibly active in the day-to-day goings on in the Realms, suffice to say it's not a good idea to get on his shit list, as Acererak soon found out.
In-Universe Biography[edit]
Known as the Shadow King, the wizard who would become Larloch grew into power and became the ruler of the Netherese Enclave of Jiksidur. He was already a Lich when Karsus' Folly happened, and as the magic failed he jumped on the blue dragon Aungahlaumitor and made his escape.
Now homeless, Larloch went Enclave-shopping, and eventually discovered the ruins of another crashed Netherese enclave caled Orbedal, which was ruled by one of his old rivals Rhaugilath the Ageless (one of the few rare Lawful Good Liches out there). Larloch dug him out, defeated him, made Rhaugilath his first lich follower, and set up shop. Orbedal was renamed Larloch's Crypt, though the passage of time and language drift had corrupted it to Warlock's Crypt.
Countless adventurers and foolish Red Wizards of Thay had tried to raid the place. All failed. They now either serve as decorations, or undead servitors of Larloch. He's become friendly with Szass Tamm however, enough to "loan" him two massively powerful artefacts for use -- the Death Moon Orb and Tharkosil's Seat.
Larloch has ben otherwise been pretty quiet as far as uber-powerful liches go, barely reacting when the Spellplague hit. He did try to recently ascend to the vacated position of God of Magic by draining the Mythals of Candlekeep and Myth Drannor, but both Elmister and the Srinshee stopped him before he could do so.
Meta[edit]
For all his infamy, Larloch hasn't been truly statted out, as Ed Greenwood had always kept him as this looming threat in his local campaign with the Knights of Myth Drannor, giving him a vague "around level 46" power range.
In 2nd Edition's Volo's Guide to the Sword Coast, he was given a level range of a level 26 Wizard, which while impressive doesn't make him stand out more compared to, oh, the Liches of the Twisted Rune, or even non-Lich Halaster Blackcloak (who was a Wizard 29).
The 3rd Edition Forgotten Realms Campaign Setting book gave a try at trying to stat him... with mixed results, especially since this was during the time where writers were trying to figure out just HOW an Epic-level character is supposed to be set up.
For stat-crunchers, the results were pretty underwhelming. He was listed as a Wizard 20/Epic 12, with a CR of 34 due to his Lich template, BUT both his stats and his skills were badly optimized, and depending on who you ask, he has even less equipment than an NPC of his threat level should have.
Do take note though, these same stat-crunchers often forget that Larloch has a lot of other intangibles that add to his threat level, such as being in control of an entire crashed Netherese enclave (and all its powerful magic), and a stable of up to 60+ (!!) other liches of varying levels and potency. Never mind a vast network of mortal followers and contacts.
Despite 4chan would like you to believe, there's no evidence for him being a direct inspiration for Overlord's Momonga/Ainz Ool Gown.