Final answer:
The relative of house-elves known for stealing food from humans isn't clearly defined in folklore. Creatures like brownies or hobgoblins in English folklore, and elves or fairy folk are considered similar to house-elves in behavior, including potentially stealing food.
Step-by-step explanation:
The relative of the house-elf known for stealing food from humans that cross them is not explicitly described in well-known literature or folklore. However, various creatures from different cultural backgrounds have traits that resemble the act of stealing food from humans. For instance, in English folklore, there are stories of brownies or hobgoblins that help with household chores and, in some tales, might help themselves to food if they are not properly appeased.
Similarly, the creature that comes closest to a house-elf in terms of behavior and magical ability within mythological contexts might be elves or fairy folk, who are occasionally depicted as mischievous and could potentially steal food. It’s important to note that none of these creatures are directly referred to as relatives of house-elves, but they share some characteristics.