Over time, leprechauns have been depicted as symbols of good fortune, or at least creatures with the power to do some sort of good, but they have also been portrayed as mischievous beings who can cause damage. Because leprechauns aren't real, they can't literally be said to be good or bad luck, but even in the fictional realm, there isn't a clear answer on where they fall on the good versus evil scale.
It's clear that belief in leprechauns can be traced back to Irish folklore, but aside from appearing as small, male fairies, there isn't a lot of uniformity in the way leprechauns are described. Some farmers apparently believed that these creatures could bring them a good harvest, and they left alcoholic offerings for the little guys. Other depictions of leprechauns portray them as moody and vengeful, with the power to cause physical damage and even death to humans who cross them. In some narratives, leprechauns are described as being magical shoemakers, a relatively banal occupation that can't really be said to be either good or evil.