Minecraft Mob: The Imprisoned
Locked away in the deepest recesses of the Strongholds' many cells of the jails within, their humanity is already lost and they no longer desire freedom beyond anything other than to kill the intruders who enter this district.
They're sickly green, their thin hair is scraggly and limp like the stands of a mop, their tunics are ruined, their white beards are shaggy, and their nails are sharp and overdue for clipping.
They've long since broken out of their wall-bound shackles, with only the short, dangling chains remaining as remnants of them once being bound to the stone cold brickbuilt walls.
Do not let them bite you, and do not let them scratch you, they're not well on matters concerning their health.
Their shackles that were dropped by them can be used to create chains, and some who wield weapons can drop chainmail armor since they were prisoners of war in a different time. Long different from before the miner, that is you, were born into whatever world you spawned in.
Listen with your ears to the clinking and dangling of their chains, it's a sign they're nearby in the prison area of the Strongholds.