Origin: Eko learned Charlie carried a Virgin Mary statue and demanded he lead him to where he'd found it.
Since Then: Charlie began following Eko, inspired by his faith. He asked Eko about baptizing Aaron and helped Eko build a church. When Locke and Desmond locked themselves in the Swan, Charlie fetched dynamite, and the two together tried to blast their way in. Charlie later helped Locke save Eko from a Polar bear.
Origin: Eko watched the Swan Orientation film and shared Locke's interest in it
Since Then: Locke and Eko bonded as men of faith, and Locke even once dreamed from Eko's point of view. The two talked of the island, including their two encounters with the smoke monster. Locke visited the Pearl and lost faith in the Swan, but Eko continued to believe "more important than ever." He expelled Locke from the station, humiliating him. Locke managed to lock Eko out of the station, leading to the discharge. Eko ended up in a Polar bear cave, and Locke saved him after receiving another dream vision. Eko died soon after at the hands of the Man in Black.