"I had you built! I sent you topside! I took you back, showed you what you was, what you was capable of! Even that life you thought you had - that was something I dreamed of and tattooed inside your head! Now if you don't call that family, I DON'T KNOW WHAT IT IS!"
Opposed to Andrew Ryan's methods and regulations on what could and could not be brought into Rapture, Frank Fontaine started out small. He initiated a smugglers' ring, sneaking in contraband goods while at the same time filling the role of businessman as head of Fontaine Futuristics. When ADAM became the next big thing, Fontaine began marketing it through plasmids and gene tonics, hiring a research team to speed up the process.
While Ryan was initially pleased with Fontaine's progress, he changed his tune after learning of Fontaine's organized crime. With tensions rising between the two, Fontaine plotted his scheme to take control of Rapture. He had Ryan's illegitimate son psychologically conditioned to respond to key phrases, then sent him to the surface. Having faked his death in a shootout, Fontaine left the public eye, leaving Ryan with a sense of false security and some of the working class citizens with a sense of discontentment.
Fontaine then reemerged as Atlas, an Irish man who appeared to be a hero for the common man. Atlas and his followers incited a rebellion against Ryan, sparking the Civil War of Rapture and sending the city into a downward spiral. But he had no means to exit Rapture, so Fontaine/Atlas activated his sleeper agent, Jack Ryan, setting in motion the events of the first Bioshock.
Fontaine is certainly more memorable through the mannerisms of his Atlas alter ego. His aims are that of power and greed, though he is willing to sacrifice any number of lives to get there. He manipulates his sleeper agent and eventually attempts to send him out with a slow and painful death once Tenenbaum comes to Jack's aid. Fontaine is a criminal mastermind, and his plans to overtake the city nearly succeeded. My only complaint is that his final boss fight is way too easy, despite the fact that he does look pretty cool as a monstrous version of the statue on the cover of Ayn Rand's Atlas Shrugged.