When talking about Easter Island everybody knows the moai, the strange stone statues scattered around the island. There is a lot of mystery behind those statues alone. But there is a lot more to the island than a strange stonework.
The isle of Rapa Nui is one of the most remote inhabited places on Earth. The closest inhabited place is 2000 kilometers away and the nearest continental point in Chile is over 3500 kilometers away. So it truly is in the middle of nowhere, surrounded by empty ocean. So it's a wonder that humans found their way there in the first place.
The island has been inhabited at least from 12th century. The dominant theory suggests Polynesian origins, but there are competing theories like Thor Heyerdahls theory of South American origins, which he proved possible with the famous Kon-Tiki voyage.
During the half millenia between the first settlements and when the island was first "discovered" by Spanish explorers the Rapa Nui people developed interesting culture. The maui are from the earlier era, assumed to be part of the tradition honouring ancestors. The bird man cult is the later development before the final collapse of the civilization before the arrival of conqerors which further affected the collapse and disappearance of a lot of evidence from the earlier culture.
A good example of this is the rongorongo, an unique pictographic writing system. There are only 26 known writings left today, mostly due missionaries wanting to destroy all evidence of earlier religions. The fact that it was usually written in pieces of wood made it also easy to get rid of the writings. To date it has still not being deciphered and the last person who knew the language died almost 200 years ago. Now only Makemake knows.