It is the same Leprechaun in all the filmsDespite the fact that the Lep appears to be of a different age and/or die in each film, I still posit they are the same one. He says he's 600 years old in the first film, but 1000 years old in the second, but maybe he was lying about his age (it could be a sensitive subject) in the first film. His weaknesses seem to change from film to film, but none of them contradict each other (he can be weak to wrought iron and clovers and destroying his gold, just as Superman is weak to kryptonite and magic). He dies at the end of several films, but he may very well have very advanced healing powers.
It is a different Leprechaun in all the filmsThe Leprechaun in part 1 melts, the Leprechaun in part 2 explodes, and the Leprechaun in Part 3 burns up. Since the Leprechaun couldn't even grow his eye back and had to steal a new one from a cop, it's safe to assume all those Leprechauns are fucking dead.
The Leprechaun is Superman's enemy Mr. MxyzptlkHe has existed for thousands of years, is magical, tiny and sarcastic, and is now experimenting with being evil. Endor Holocaust, Wicket was captured and tortured by remaining Imperials for his role in the destruction of the Death Star. They scorched his body with blasters, permanently burning off much of his hair and causing his mind to snap. He was, however, able to remember a few Jedi techniques he picked up from Luke Skywalker, and he used them to kill his captors and escape in a small spaceship. He flew long and far before his craft eventually ran out of fuel and crashed in Ancient Ireland. He fled into the woods, where he eventually learned English, cobbling, and earned quite a bit of gold. Protecting that gold with the Dark Side Of The Force, he eventually gave rise to the legend of Leprechauns.