Undead appeared after a particularly powerful Old Lord was slain in battle and the gift of life and resurrection was given to the people on the battlefield, slain and destroyed. Their essences flew back to them, and consciousness restored. It’s harder for an undead to be created from a fleshy body, just because the body is fighting it’s soul coming back in. Rotted/mummified bodies are much easier to resurrect. Also, souls can return to a body and have the body added to by other corpses without souls, and be modified, armored, and experimented on with relative ease. Thus, undead can grow to enormous sizes. Undead can also smell when death draws near, and some civilizations/communities use undead as hounds to sniff out the survivors of battles.
Undead culture is heavily based off of ways to keep busy. With time being a relatively un-important concept, being occupied and for one’s efforts to not go to waste are most important.
Undead, or “second-timers” as some refer to them, obsessively collect things; henceforth, they’re unburdened by fashion fads and the popularities of time period. They will often layer many sets of clothing scavenged from battlefields, as they are want to do. Undead find solace in welcoming new bodies to the afterlife.
This particular individual is what’s known as a “Reaver”, one who (usually) harmlessly picks through the spoils of war and battle for hidden riches that even corpsmen won’t touch.