Lich

A Lich is a powerful wizard who was sealed away, usually because their enemies didn't know how to kill them.

The Rites of Fortification make most wizards extremely difficult for mundane humans to kill. In civilizations without access to Orichalcum, sealing a wizard away somewhere remote is often the best available option to remove a disruptive wizard.

Liches are not a common occurrence, and can vary widely in power level. Generally speaking, the longer a lich has been entombed, the less of a threat it represents. Advances in both magic and technology mean that older liches typically command more rudimentary magic, but were entombed because anti-wizard technology was also much less advanced. For example, very few liches from the pre-gunpowder era would have the proper fortifications to survive a gunshot to the head or torso. In addition, older liches will have greater complications resulting from Chronophilia and isolation-related mental illness.

Uncovering a lich typically varies from a setback to something akin to a natural disaster.

An-Namrood the Eternal spent the fifth and sixth century as a lich after the fall of the Reman Empire. He was disentombed in the early seventh century.

Ceskan Incident
There is an apocryphal story of an Eldest lich being uncovered by humans at some point in the 14th century. Details on the story vary, but the most common elements are as follows:

An expedition in the 14th century discovered an untouched tomb a few days ride from the city of Ceska. Upon opening the tomb, the prospectors torches all brightened noticeably, and the air had a different smell to it, one that would not be attributed solely to must. Inside the tomb, they discovered a living Eldest, sealed away for all this time. The Lich killed the majority of the crew and ran to the surface. The survivors followed, trying to escape the tomb. They heard the Lich breathing heavily during its climb. Upon reaching the surface, it began to hack and wheeze, unable to catch its breath. It died a few minutes after reaching the surface, apparently of asphyxiation, as if it couldn't breathe the air.

This story is regarded cautiously in scholarly circles. The notion that an Eldest wouldn't have been able to breathe modern air is a strange conclusion for a folktale to draw, and there is some evidence of the truth to this claim. However, many details of the trip--even basics that like where and when the expedition occurred--are unknown. Most tellingly, neither the site of the tomb nor the skeleton of the dead Eldest have been recovered. As complete Eldest skeletons are unheard-of, let alone one that hadn't fossilized, such an item would almost certainly be unique and of great value to any collector or scholarly institution. Even owing to its great size, the fact that no non-fossilized Eldest bones have ever been documented casts suspicion on this story as fiction.