A ruthless killer的用法和样例：
- Perhaps Genghis Khan would appreciate this more than his traditional reputation as a ruthless killer.
- Look at the riot of flowers -- full of vitality; no one, not even a ruthless killer, would be able to raise a finger to them.
- A ruthless speculator or adventurer.
- He ate in a ruthless manner,champing his food.
- The painting portrays him as a ruthless conqueror.