Leprechaun

Leprechauns are little men who live in the farmhouses and wine cellars of Ireland. These green-clad cobblers love a good time--they are often drunk, and are always good-natured. They make shoes for elves (but always just one, never a pair), and are even known to do some chores for humans. Each leprechaun guards a treasure left by the Vikings who invaded Ireland long ago. If a human manages to catch a leprechaun--which is a very difficult task--he will give his treasure to the human as a bribe to let him go. However, if you catch a leprechaun, do not take your eyes off him for a second, or he will disappear.

Sources

Encyclopedia Mythica: Leprechaun

A Field Guide to Irish Fairies