Slayer (noun)

1. A person who kills another, especially in a violent way.
2. A person or thing that defeats or destroys something.

Origin:

Old english sleágere, from sleán "strike, slay", of germanic origin; related to slay.

Examples:

1. The police are hunting for the slayer of the young woman.
2. The dragon was a fierce slayer of knights.
3. The virus is a ruthless slayer of the elderly and vulnerable.
4. The dragon slayer was a hero in the medieval tales.
5. The disease was a ruthless slayer of the population.