Most of the individuals who came to Rapture were people that Andrew Ryan knew personally. Others received an invitation to become part of the city. Or were hired to work on its construction & never left. See "There's Something in the Sea" for the "The Vanishing", which mentions the mass disappearance of quite a few notable people who ended up in Rapture.
Amongst the examples is Bill McDonagh. He, as revealed in the Audio Diary "Meeting Ryan", became a close associate of Andrew Ryan after he was hired to be Ryan's General Contractor, on a building he owned in New York.