Vecna (his name is an anagram of the last name of Jack Vance, the man who invented the "fire and forget" rules for magic used in pre-4e) is one of Evil deities in D&D, having become considerably more powerful over various editions. He also assraped reality itself, punking the major powers of Ravenloft, Greyhawk, and Planescape in rapid succession so hard that it resulted in third edition, where fullcasters like him were overpowered beyond belief Just as Planned, and even after being beaten by the typical plucky band of adventurers, he still got a net gain in power from Demi-god to Lesser god, double Just as Planned. If there is a Doctor Doom equivalent in D&D, it is Vecna, fucker's the most intelligent being of mortal origin ever and unlike Asmodeus who constantly says he's all smart and wise and awesome but has accomplished precisely dick out of hell besides maintain the status quo, Vecna actually goes out and gets shit done and utterly buttfucked the Status quo.
Born in the human city of Fleeth, Vecna was taught magic by his mother. The authorities were not amused and executed her for witchcraft. The young Vecna fled and continued his study of magic. Over a thousand years later, he had become a powerful lich and laid siege to Fleeth. Officials approached him and offered their lives if he'd spare the citizens. Instead, Vecna let his army murder everyone in the city, except the officials.
As he began a ritual to ascend into godhood, Vecna was betrayed by Kas, his most trusted lieutenant. In a climactic battle that cost the lich his left eye and hand, Vecna reached apotheosis followed by an explosion that leveled the new god's empire and flung both of them across the planes.
Vecna is the Evil god of Undead, Necromancy and Secrets. Specialising in dark magics and undeath, he is the go-to guy for necromancers and dark mages of all sorts.
There are various artifacts associated with the Maimed God, including the Eye and Hand of Vecna, the 3e artifacts the Fingers, Incisors, Molar, Scalp, Skin, Heart, Left Foot, Left Ear and Right eye. These appeared for only one edition, because things like the Foot of Vecna sound stupid. Also included is the elusive Head of Vecna.
Vecna has no permanent home, not in the Astral Sea, the Abyss, Shadowfell or anywhere else. He and his followers travel the planes in search of knowledge, artifacts and power. He always travels out of sight and in the dark to avoid attention, prefering forgotten libraries, ruins of lost civilisations, Shadowfell and the Planes. Vecna does hold strongholds in several locations, but they are either far away or well-hidden from civilisation, or are located in dangerous areas, such as Pandemonium.
Vecna has the desire to rule over all, living and dead. He is worshipped by all those who desire knowledge and that which is not meant to be known. Undead that are not in service to Orcus are almost always in service to the Maimed God. He commands all sorts of undead, from run-of-the-mill zombies and skeletons to Oni, Liches, Vampires and various kinds of constructs. His followers often band together in cults, dedicated to the practice of necromancy, finding secret knowledge, or both. These cults build their own altars and places of worship to their lord.
There are some who stand out in service to (or against!) their lord:
- Acererak is the Demilich in charge of the Tomb of Horrors. Only his head is in the Tomb though (or more specifically, a copy of his head). The rest of him is in Shadowfell, working on a spell to control undead everywhere.
- Osterneth appears as an attractive woman in her late 20s, but is actually a lich, bearing Vecna's heart in her chest, and is one of Vecna's most trusted allies.
- Kas the Betrayer is a vampire lord that schemes against Vecna. He was the one to maim the Maimed god, in an attempt to attain divinity himself. His weapon, the Sword of Kas, roams the planes and is the only weapon believed to be able to kill Vecna.