George Lucas discovered her
Or at least, he gave her her big break.
This information comes from Kathleen Turner herself, in an interview given circa 2004. When she auditioned for the part of Matty Walker in "Body Heat," Lucas, who produced the film uncredited for his friend Lawrence Kasdan and apparently had some say in the casting, watched Turner's audition tape and said, "No more auditions. She's Matty."
Since it is all but illegal on IMDB.com to say anything even slightly complimentary about George Lucas, I thought I'd toss that out there. Let me guess: the too-hip-for-words posters will say, "Well, that proves what a moron he is, because look where Turner is now!" Oh, I don't know. Maybe she hasn't aged well and her career has declined in recent years, but her performance in "Body Heat" made her a star and is still indelibly marked in moviegoers' minds, and she followed it up with many other fine performances.