There were five movies I believe.
In the first movie a man captures a leprechaun and acquires his pot-o-gold. He takes the gold home not realizing that the leprechaun has followed. The leprechaun goes on a killing spree to get his gold back. The gold keeps falling into more and more people's hands so the leprechaun has to keep killing to get it back. Each movie is pretty much the same, but different people, different ways to die, etc. They're actually pretty good, if not a bit redundant.