The Lich, Demilich & Boneclaw - Evil Immortality

A Lich is a powerful undead monstrosity created by a process it itself volunteered for. When a mage of any kind reaches a point that they feel that they don't have enough time left, they will beseech a demon, devil, or evil deity to gain the knowledge that will let them live forever. 
Each Lich will build a phylactery and place a victim's soul into it, which has spells written or carved on the inside. When this is done, the Lich drinks a poison that will kill it, and force the soul to be devoured by the phylactery. During this process their own soul will be placed in the phylactery, and a new body will be available for it to inhabit. When successful the Lich is now able to carry on, as long as the phylactery is fed with souls regularly. Each time it doesn't a piece of the Lich is destroyed, and when not fed, the Lich in time is turned into a Demilich. The latter form is a skull with gems in it's teeth and fills these up when on victim is killed. The Demilich feeds on these regularly to stop itself dying.
Every time a new Lich rises it will have a complex where it's phylactery is hidden away behind henchmen and traps to stop anybody getting to it. Destroying it is the only sure-fire way to kill the Lich, for if it's body is destroyed, then it reforms after a number of days later. The Lich will continue to accrue spells, and magic items, and many are able to create their own followers, usually through summoning demons, devil, or elementals, and also building constructs or undead too, depending on the individual. As with many undead, the individual Lich can be decades, centuries or even millennia old. Some of the oldest belong to the Council of Thirteen, the ruling council of an organisation called the Necrocult. These individuals are at least centuries old if not longer. They are spread throughout the world using magic to keep in contact, and trying to bring about an apocalypse, turning all life on the planet into undead minions. Many seek out this cult both to join or destroy it, and few have ever came close.
Sometimes the process fails, and the Lich is stuck, unable to continue with it's plans. When this happens the spirit of the Lich attaches itself to the nearest evil creature and becomes a minion of it. This can be anything from a cruel raider, to a bullying town mayor, or even a self-centred spiteful child. It hunts down the opponents of the person, whether they are aware of this or not. Sometimes the Boneclaw makes it's appearance known and takes commands from it's new master, or they have no awareness of each other, just a vague memory of who needs killed. If and when the person ever dies, then there is a better than average chance of the Boneclaw dying too. After all the link is permanently severed.