Atlas is the name used by the mysterious renegade that would eventually cause a full rebellion in Rapture, forcing Andrew Ryan into hiding.
Information regarding Atlas' past is almost non-existent. To the player, Atlas is a guide through the depths of Rapture and a constant help in the fight to overthrow the megalomaniac Andrew Ryan but even through that we learn very little about him. What we do know is that he's a married father of one, perhaps an Irish immigrant contracted by Fontaine Fisheries as a laborer. Whatever his job was he experienced the hypocrisy in Andrew Ryan's Utopia first hand, causing him to quit and begin a personal crusade against Ryan. He started off by gathering together a band of followers in the poor houses of Apollo Square where he and his family lived, after a while this group grew beyond Ryan's expectations causing him to lash out against Atlas.
Atlas responded by rousing his people into a frenzy, which would cause a riot in Rapture like they'd never seen before. The fight lasted for so long that it drove Ryan into hiding and eventually caused a massive uprising on New Years Eve 1959. This uprising caused the downfall of Rapture as a society and created the state of Rapture as Jack (the player) sees it in 1960.
The protagonist's only friend in Rapture 'Atlas" is revealed to be Fontaine towards the end of the game, who has been manipulating the player to do his will.With the use of the hypnotic trigger phrase "Would you kindly..." he is able to force you to eliminate his only competition, Andrew Ryan so he can take over Rapture. Frank Fontaine admits that the character "Atlas," the crusading reforming leading a rebellion against Ryan's increasing authoritarianism as his Ayn Rand Objectivist paradise spins wildly out of control, is nothing more than a cynically created long con. Atlas is nothing more than part of Fontaine's master plan to seize control of Rapture by turning the poor, the disenfranchised, the people who showed up believing they would be captains of industry but ended up pushing brooms, against Ryan. While Fontaine attacks Ryan through smuggling and his own industries such as plasmids and fisheries, his Alter ego attacks Ryan as the political leader of Rapture through Atlas.
Fontaine consumes so much Adam that he becomes an almost God-like figure and the main character has to battle it out against Fontaine at the end of the game. Fontaine is eventually overrun by little sisters extracting Adam from his body and is killed.
Frank Fontaine is voiced by Greg Baldwin who also donated his vocal talents as the grossly unpopular Norton Mapes from F.E.A.R.
The Smuggler Of Rapture
Fontaine came to Rapture a poor hood from The Bronx with nothing but big ideas about how he would turn himself into a millionaire. Within a short while he owned and operated "Fontaine Fisheries", a fishing company that also doubled as a sophisticated smuggling ring.
In Rapture it was illegal to own things like Religious texts, music and art from the surface unless it was given the official O.K by Andrew Ryan. This so disgusted Fontaine that he used his surly band of sea merchants as smugglers, creating a massive criminal empire. He kept the smuggling under wraps, though by disguising himself as a legitimate businessman with interests in charity (Fontaine's Home for the Poor) and Applied Sciences (Fontaine Futuristics). Andrew Ryan refused to trust Fontaine however and asked Police Chief Sullivan to keep a close watch on his activities, especially the work he was doing at the docks.
Andrew Ryan would develop an admiration for Frank when his fisherman discovered the sea slug that produces ADAM, a chemical that would enhance the human body beyond its normal capabilities giving the user powers such as levitation or the ability to produce lightning. It was this discovery that lead him to form a relationship with Bridgette Tennenbaum who would create a commercial form of ADAM that could be sold via Fontaine Futuristics. Ryan saw this as an example of the kind of free enterprise that he had been preaching about, Fontaine was Ryan’s ideal businessman-- Smart, quick to the point, and ruthless.
Ryan's admiration would not last long however. His Police Chief had done some snooping and had found Fontaine's smuggling ring, which launched Ryan into a state of intense fury, demanding Fontaine to be assassinated as a traitor by Sullivan’s police force. When Fontaine caught wind that he was being targeted he developed a plan with Dr. Suchong to take over Rapture involving Ryan's illegitimate son and brain washing technology developed by Fontaine Futuristics.
Ryan had Fontaine assassinated in the late 50s, which caused the workers of the docks to become mad with splicing, swearing revenge against Ryan. It would be a couple of years before a young Irishman would fulfil their need for vengeance...
In the paradise of Ayn Rand objectivism attempted by Andrew Ryan, Fontaine, and his Alter Ego Atlas, represent the inherent flaw of the world of Rapture and the means to Ryan's tragic demise. The "Great Chain" of rapture did not withstand the criminal element that took enlightened self interest in its own direction and as Rapture became less Ryan's vision, he himself became more authoritarian and violent, destroying his own principals. Fontaine and Ryan, while rarely ever seen and portrayed mostly as voices communicating with the main character, are two of the most sophisticated characters in video games.