Francine Pascal (born today in 1938) grew up showbiz-adjacent in Queens (her brother Michael Stewart wrote the book for Hello, Dolly!). But after a stint writing for soap operas, Pascal made her mark in a different format. In 1983, she had an idea for a teen soap opera about 16-year-old twin sisters (good Elizabeth and more risqué Jessica). An eager publisher snapped up the idea. Ghost writers were hired. Pascal was in charge of outlines, characters, inspiration, and continuity.
The first Sweet Valley High paperback was released that year. Their popularity smashed records and birthed a new subgenre (The Babysitter’s Club, et al). In 1985, Perfect Summer became the first New York Times-bestselling young adult title. By the time the series ended in 2003, it had published 152 titles and sold roughly 250 million copies. After all those stories, though, the sisters never managed to reach their seventeenth birthdays.