Frank Fontaine is the revolutionary who led the working class of Rapture against Andrew Ryan in a Civil War before the events of BioShock. After the nationalization of Fontaine Futuristics, the disillusioned Fontaine, believed dead and now disguised as Atlas, stood up in protest against Ryan Industries founder Andrew Ryan and began the Rapture Civil War in 1958, which ravaged the city.
At the beginning of BioShock, Atlas is believed to be a family man who came to Rapture in search of a better life for his family. Guiding Jack through the wrecked districts of Rapture via a shortwave radio, he says he needs Jack's help to rescue his wife Moira and infant son Patrick, who both are trapped in Rapture.
It is later revealed, towards the end of the game, that Atlas is actually Frank Fontaine, the arch-nemesis of Andrew Ryan, who had brainwashed Jack to get to and kill Ryan.
