When Richmond medical examiner Kay Scarpetta plunged her scalpel into a corpse for the first time more than a quarter of a century ago, her creator, Patricia Cornwell, had no idea that big things were in store for both of them. In the first several novels the former crime reporter wrote, all unpublished, Scarpetta — blond and beautiful, detail-oriented and driven — wasn’t even the protagonist.

When she finally saw print as the heroine of Cornwell’s first published novel, 1990’s “Postmortem” — which swept that year’s mystery-novel honors, including the Edgar, Creasey, Anthony and Macavity awards — it still wasn’t immediately clear that she would become one of the most popular characters in the history of crime fiction.

“I wasn’t thinking that far ahead,” recalls Cornwell, whose manuscript was rejected by several New York houses before being accepted by Scribner. “I just thought it was a dream that I was actually getting published.”

Since then, the Scarpetta books have sold an astounding 100 million copies in 35 languages in 120 countries, with “Red Mist,” the 19th of the series, making its debut at No. 2 on The Washington Post’s bestseller list Sunday. A Scarpetta movie starring Angelina Jolie is in the works. And Cornwell — touted by her current publisher, Putnam, as “the world’s No. 1 best-selling crime writer” — is firmly established as the creator of one of the publishing industry’s most durable and lucrative franchises.

No one is more surprised than Cornwell herself. “It’s like running on a track, you know, and at some point you stop and ask yourself, ‘How did I do so many miles?’ ” she says in an interview from her home in Boston. “Nineteen Scarpetta novels — yes, I know, it’s shocking. When I see all my books in a bookcase, it makes me really tired.”

“The biggest risk with a series that goes on this long is that you’ll get bored with the character,” says author Patricia Cornwell. “I’m just grateful I’m still interested, and that the readers are, too.” (Gina Crozier/Gina Crozier)

Not that tired. As she spoke, Cornwell was preparing to leave for her “Red Mist” book tour, which kicked off last month in the United Kingdom; the American tour, which includes stops in New York, Phoenix, Los Angeles, San Diego, Portland, Dallas and Florida, is ongoing. And she’s already at work on a 20th novel featuring the character originally known in some circles as “the female Quincy,” after the forensic pathologist played on TV by Jack Klugman.

“The biggest risk with a series that goes on this long is that you’ll get bored with the character,” says Cornwell, 55. “I’m just grateful I’m still interested, and that the readers are, too.”

What accounts for Scarpetta’s longevity? The most obvious answer is that, as she has from the first, Cornwell packs every novel with what seems to be insider information — about the latest technologies and strategies in forensic pathology and the ways they can reveal the secrets of dead bodies, including how they got that way; about the procedures of police, the FBI and the military; and about the psychology and methods of criminals.

These last, in the case of “Red Mist,” include some very scary poisons and — perhaps — intentionally botched prison executions leading to fates far worse than death. In the new book, Scarpetta finds herself in Savannah, Ga., where she visits an inmate in a women’s prison and becomes interested in a series of suspicious deaths there. She also ends up investigating the horrendous killing of a Savannah family several years earlier, a crime for which it appears the wrong person has been convicted.

Another reason for Scarpetta’s stamina as an object of fascination, both for her creator and for readers, is that she has evolved considerably over time. In the early novels, she could be “prickly,” as reviewer Marilyn Stasio put it in the New York Times, and so caught up in her work that she forgot to be human, even with the people closest to her — including her FBI agent husband, Benton; her Everyman sidekick, Marino; and her computer-geek niece, Lucy. More recently, a kinder, gentler Scarpetta has emerged.

“She was pretty isolated in the earlier books, but now she’s mellowed in some ways, and her interaction with the other characters has gotten more interesting,” Cornwell says. “She’s more of a caretaker than she was, more understanding and protective of the people around her. She’s older, of course, and as you age, you become vividly aware of how important your connections are. She’s built a family of sorts, and that’s important, because the books aren’t just about the nuts and bolts of forensics anymore. They’re more about walking into a room where Marino is and wondering why he’s looking at her that way.”

Scarpetta is also more vulnerable, more psychologically transparent than she once was. Although she presents herself to the world — to her adversaries in particular — as supremely confident, in fact she is a worrier, prone to self-doubt and feelings of culpability for outcomes beyond her control. “You tend to feel guilty about a lot of things that have nothing to do with you,” Benton tells her, with his typical bluntness, in “Red Mist.” “You think it’s your responsibility to fix things. Or prevent them. You always have.” (Not that she enjoys being analyzed, especially when it’s so spot-on. “I see,” she snaps. “When I think I can make a difference, I should never trust it.”)

’Red Mist’ is Cornwell’s 19th book in the Kay Scarpetta series. (Putnam)

The new wrinkles in Scarpetta’s character are derived, in part, from those of her creator. As Benton points out in the new book, his wife’s Atlas complex is related to her difficult relationship with her father — a clear echo of Cornwell’s own history. Her late father, a lawyer named Sam Daniels, walked out on the family on Christmas Day when she was 5 years old.

“In that magical-thinking sort of way, it had to be my failure, because if he’d loved me enough, he wouldn’t have left,” Cornwell recalls. “We were never close after that, even though he had a daughter from his new marriage and treated her like a little princess. Of course, his feelings toward me were colored by the fact that he hated my mother. But no one ever said to me, ‘This is not about you.’ I guess I’m still working on that.”

And so is Scarpetta.

Then again, Cornwell has bestowed aspects of her personality and background upon other characters, as well. Like Benton, she can be cerebral to a fault. Like Marino, she’s capable of snap judgments and “leaving my things lying all over the place.” Like Lucy, she’s a helicopter pilot and a devotee of Harley-Davidson motorcycles. And like Jaime Berger, a lawyer who makes a return appearance in “Red Mist,” Cornwell was once married to a man, then got a divorce when she fell in love with a woman. (She is now married to Staci Ann Gruber, a Harvard educator.)

Scarpetta’s movements have also mirrored her creator’s. After several years in Richmond, Scarpetta moved on to new posts in Florida, South Carolina and, most recently, Boston. At one point in “Red Mist,” Scarpetta reflects that she had “no business” in Richmond, “the capital of the Confederacy.”

“I think politically she does better in Massachusetts,” Cornwell says. “Some areas of the South she has trouble with, just like I do. She prefers someplace that’s more live-and-let-live, where there aren’t so many judgments about people’s race, religion or sexual orientation. I don’t want her in a place where she has to deal with that all the time.”

Cornwell and Scarpetta are one, then — a fact reinforced, in “Red Mist,” by the author’s return to the first-person point of view. The Scarpetta series began in first person, then shifted midway through to third person, which allowed Cornwell greater freedom to inhabit the minds of other characters. But this had unforeseen consequences that she came to regret.

“I went to third person because I wanted the ability to take on all these other personas and show the reader things that Scarpetta doesn’t experience herself,” she recalls. “But as I gradually realized, when I was showing those things, as in ‘Predator,’ it could be very frightening. In the third person, I was in the persona of the people doing these violent, disgusting things, and it made me really uncomfortable. When I shifted back to first person, it was like returning to someone I hadn’t visited in years. It was much more comfortable, for me and for the readers. In the first person, the readers feel smart, like it’s them solving the case. And because they’re holding her hand, so to speak, they feel safe, even when bad things are happening in the story.”

Cornwell’s concern for her readers — with whom she’s in direct and regular contact via Facebook and Twitter — should reassure those who might be concerned that author and character, after so many books together, might tire of each other’s company. Scarpetta will never suffer the fate of her distant ancestor, Sherlock Holmes, whose creator, Arthur Conan Doyle, got so bored with the famous sleuth that he killed him off (only to resurrect him a few years later after an outcry from the detective’s legion of fans).

“I can’t imagine doing that, and I never would, because it would traumatize my readers,” Cornwell says. “As silly as it sounds, these characters are very real to the fans, as I discovered from the firestorm that happened when I killed off Benton.” (Scarpetta’s husband died in 1998’s “Point of Origin,” then reappeared, after what Cornwell calls a “hue and cry” by readers, in 2003’s “Blow Fly.”) “An author who doesn’t care about the readers is foolish.”

Patricia Cornwell, like Kay Scarpetta, would never make such a rookie mistake.