marauder
A person who roams around attacking or stealing from others.
A marauder is someone who roams around looking for things to steal or people to attack. The word comes from an old French term meaning “to prowl,” and it captures that sneaky, dangerous quality of someone moving through an area searching for opportunities to raid or plunder.
Throughout history, marauders have been a serious threat. Viking marauders sailed along European coasts, attacking villages and monasteries. Marauding bandits hid in forests, ambushing travelers on lonely roads. During wars, soldiers sometimes became marauders, stealing from civilians instead of following orders.
In stories and games, marauders are often roving villains who show up unexpectedly. They're not organized like an army or settled in one place like a gang of thieves in a city. Instead, they move from place to place, taking what they want and disappearing before anyone can stop them.
You might also hear the word used playfully. A teacher might joke that “marauding squirrels” keep stealing birdseed from the feeder, or someone might call their hungry siblings “marauders” after they've raided the kitchen for snacks. But the word still carries that sense of sneaky, unauthorized taking, even when used in a lighthearted way.