Zombie Villager
In Better Than Wolves, all Villagers in the world will spawn as Zombie Villager.
Unlike the player, they are unaffected by terrain speed modifiers. This makes them quite dangerous, as they will be able to catch up easily.
Despite their dangerous nature, they are a fundamental part of the mob, since part of the mod's tech tree is gated behind Villager trading.
Curing
To cure a Zombie Villager, the player will have to make Soul Urns and and throw it directly at him. It will turn into a regular Villager in less than a day.
There is no way to know the profession before curing the Zombie Villager, and since their profession is determined before the curing process, it is recommended to try and collect them all from a village in order to increase the chances of acquiring the desired one.
This can be difficult given the Zombie Villager's tendency to wander away from Villages.