This is a theory as to the REAL story of American Dad.
American Dad is focused on the Smiths, your average conservative family (kind of...). The household consists of Stan Smith, Francine Smith, Steve Smith, Hayley Smith, Roger Smith, and Klaus. This is the story of how they came to be.
American Dad was based on the life of Francine, who was an orphan until she was adopted by two abusive Asian parents. Her new parents also had a biological daughter, who they admired because she lived up to their expectations. Francine however, was a slacker, and beaten senseless and raped by her father throughout her childhood. She grew up to be depressed, addicted to heroin, cocaine, and hallucinogenics.
She soon began to lose her mind, she created this fictional family in an attempt to finally live in a normal household. But she didn't make the Smith family normal, she made them the way she wanted them, insane and comical. To add to the comical part, she added Roger and Klaus. In the real world however, she was dying and didn't even realize it.
She was spending weeks in her fictional world, only surviving because she was eating fictional food which she thought was real, thus causing her to not have a sense of starvation. All she wanted was a perfect family, and she created the life stories of all of her characters.
She wanted a loving husband, creating Stan. She wanted kids who bicker and fight like your average family, creating Steve and Hayley, though Hayley was made to be the unwanted child that Francine was and as I already explained, she created Roger and Klaus.
Soon, Seth McFarlane met Francine, and she told him about the family as though they were real and Seth decided to make a TV cartoon based on her story. Seth was clever, though, and to avoid people from figuring out the truth, he killed Francine, turned her into a character on the show, gave her character a background, and based the show on Stan, her fictional husband. Seth then created more characters such as Jeff Fisher, Greg and Terry, Francine's Parents, etc.
No one ever knew about Francine's death because no one cared, but God bless, and lets hope that when FOX learns this, American Dad gets shut down.