Before the coming of St Patrick there was the Tuatha De Danann. These were a race of mythical superhumans who arrived in flying longboats and declared themselves in charge. This lasts for four thousand years until Patrick arrives. By this point the Tuatha De Danann have left the shores of Ireland to take up residence in the blessed realm of Tir Na Og where they will generally live forever. They only come into the real world to visit their descendants the Fiann and have dalliances such as the tale of Oisin and Niamh.
We get most of our stories of them from the Christian monks who scribed their tales from the locals and the myths they themselves knew. Unusually they were quite nice to the Tuatha even though they were pagans. They are portrayed not as Gods but as fallen angels. They are neither evil nor good, just misguided. A fact that is born out with the tale of Oisin where he refuses to be baptised by St Patrick, opting to return to the blessed realm and his family rather than heaven.
Patricks influence on the Island is plainly apparent as the celebrations of St Patrick’s day attest to. ST Patricks day gifts, such as the ones that are available from https://www.shamrockgift.com/st-patricks-day-gifts are more common than that of Tuatha De Danann ones. They have become mythical figures that lurk in the blessed realm sometimes still coming over to the real world and causing some mayhem. Thanks to the Monks we refer to them as their new name, the Fairies.