Tangi Tereapii was installed Numangatini Ariki at a packed ceremony and feast at Te Maruata-Nui-o-Numangatini Marae.
The Cook Islands News reports the celebration was attended by the whole island, as well as dignitaries from Rarotonga, Aitutaki and Atiu.
A Mangaia resident, 77-year-old Allan Tuara, said it was one of the biggest investiture ceremonies he had witnessed.
For younger generations, he said, this would have been the biggest event of their lives, featuring many gifts, items and speeches from each puna as well as guests from Rarotonga and other islands.
As well, several 20-metre long marquees offered plenty of food for people to enjoy.
"There was so much food left and everyone was asked to take the leftover food home," Tuara said.