She is, in a sense, an American Mona Lisa—her face is widely known, but she herself is obscure. A sprightly 77-year-old widow now living in Riverside, Calif., Nan Wood Graham was the model for the farmer's daughter in the famous painting American Gothic. It was done by Grant Wood, her brother. Frowning down from the canvas dyspeptically, Nan became a symbol of straitlaced Middle America.

She is fiercely loyal to her late older brother. He helped raise her in their native Iowa after their father, a Quaker farmer, died when Nan was only 16 months old. She remembers vividly the day 47 years ago when Grant asked her to pose. "He saw a house he thought he'd like to paint," she says, "and he wanted two people in front of it who looked like they would live there. For the man, Grant chose Byron McKeeby, our family dentist. He had another friend of ours picked out for the woman, but he was afraid she would get mad when she saw the painting, so he chose me. He said he could lengthen my face so that no one would ever recognize me, but of course they did—right away."

Wood died in 1942, but the house in Eldon, Iowa has become a landmark, and the painting has assumed a life of its own. Still, Mrs. Graham (her husband, a real estate man, died in 1967) refuses to surrender herself to the public domain. She sued NBC in 1968 after a doctored version of Gothic, showing the daughter in a bikini, was featured on the Johnny Carson show. She also sued Look, which had portrayed the woman in a bra, and Playboy, which had shown her topless. The suits for a total of $9 million were settled out of court, and the money, she says, went to charity.

Despite the publicity generated by the previous suits, the April issue of the tasteless-and-proud-of-it Hustler magazine printed still another topless parody. "It was horrible," Mrs. Graham says. "I was afraid I'd have a heart attack when I saw it." Unimpressed by the standards of the unbuttoned '70s, she is suing for $10 million. "As a rule, I'm a very happy person," she says, "but something like this really gets me down. I'm only glad Grant isn't alive to see what happened. He was such a moral person, and he hated anything like that."