In 2017, her latest naughty novel, Darker, was published. According to Forbes, the book didn't fly off the shelves as fast as its predecessors. Nevertheless, it, and the continued success of her famous trilogy, helped James to earn a whopping $10.5 million (£8m) in a year.
Riordan (pictured on the left) is arguably most famous for Percy Jackson, a fantasy story inspired by Greek mythology. From June 2017 to June 2018, he sold 2.1 million books in the US and earned $10.5 million (£8m).
Nora Roberts started to write when she was snowed in in her US home during a blizzard and she began to make up stories to entertain her small children. She then turned to writing romantic fiction and her debut novel was published in 1981.
Now with a writing career spanning almost four decades, Roberts sold more than 1.5 million books in the US from June 2017 to June 2018, earning her $12 million (£9m).
Writer's block is clearly not a problem for Danielle Steel (pictured, middle) as, according to her website, she publishes six new books a year. And it appears to pay off as she made $12 million (£9m) from June 2017 to June 2018.
Michael Wolff worked as a journalist for a number of publications as well as a writer. In January 2018, Wolff published the explosive behind-the-scenes book Fire and Fury about the first months of Donald Trump’s presidency.
In three weeks alone, the book sold 1.7 million copies and earned Wolff $13 million (£10m) between June 2017 and June 2018. He's now reportedly working on a sequel.
Best-selling American author Dan Brown also taught English before taking up a full-time career as a writer. Arguably his most famous novel is The Da Vinci Code, a book about a symbolism-obsessed professor that was made into a movie starring Tom Hanks.
In 2017, he published his latest novel Origin, which features the same protagonist as The Da Vinci Code. The book helped Brown earn $18.5 million (£14m) in a year. He also teaches online writing classes.
Jeff Kinney originally wanted to be a newspaper cartoonist and he did get his work published in his university paper. But after graduating, he struggled to sell his cartoons. In 1998, he started writing the irreverant children's book Diary of A Wimpy Kid and published it online himself.
After signing a book deal in 2006, Kinney has now sold more than 200 million copies of his Wimpy Kid books. He made $18.5 million (£14m) in a year. He also owns a bookstore in Massachusetts.
Like several other authors on this list, John Grisham started on a very different career path. He wrote his first thriller novel while working as a lawyer. It was published in 1988 to modest sales of 5,000 copies.
Thirty years on, Grisham (pictured, right) sold 2.6 million copies and earned $21 million (£16m) in one year alone. He usually writes one novel a year.
Known as the king of horror, Stephen King's body of work includes classics of the genre such as The Shining and Carrie. King achieved his first professional sale of short stories in 1967, before he'd even graduated from university.
Not only has King (pictured, right) sold millions of books, but many of his novels have been turned into films, most recently It. He earned $27 million (£21m) between June 2017 and June 2018.
Now meet some people who just missed out on making an absolute fortune
Harry Potter creator JK Rowling has sold millions of books worldwide. Before creating her fantasy series, she didn't have much money and even lived on state benefits for a while.
Today Rowling has built an empire around the series that includes spin-off books, plays and movies. According to Forbes, her sales fell sharply between summer 2017 and summer 2018, but only because she didn’t produce a major book. However, she still raked in $54 million (£42m).
James Patterson was the highest-earning author between July 2017 and July 2018, pocketing an astonishing $86 million (£67m). But the American's work didn’t become an immediate success. In fact, he was turned down by 31 different publishers before securing a deal for his first novel The Thomas Berryman Number in 1976. Since then, Patterson has sold millions of copies worldwide, writing for both adults and children, and created memorable characters such as Alex Cross and Max Einstein.
Patterson holds the Guinness World Record for the most New York Times best-sellers and published 20 books in the last year alone. And one of his latest works, The President Is Missing, was co-written by none other than former US president Bill Clinton.
Do you own any of these rare books worth a fortune?