Julian May’s Christmas tree was bedecked with a flying-dinosaur ornament handcrafted by someone better known for writing “I, Robot” and other sci-fi classics — Isaac Asimov. Author Ray Bradbury used to bounce her son on his knee.

Before becoming a popular science-fiction writer herself, Ms. May grew up in a Cape Cod home in Elmwood Park, attended Trinity High School in River Forest and landed her first job at Burny Brothers bakery at 2445 N. Harlem.

Her books included two sprawling sci-fi sagas: the four “Saga of Pliocene Exile” novels and the six-book “Galactic Milieu” series. They incorporate aliens, barbarians, time travel, swordplay and paleontology, with elements of Carl Jung and Celtic and Norse mythology.

Ms. May, who wrote 19 science-fiction and fantasy novels and more than 250 young-adult nonfiction books, died of a heart attack Oct. 17 at Overlake Hospital in Bellevue, Wash. She was 86.

One of her biggest fans is Nick Dudman, the Oscar-nominated wizard of makeup, prosthetics and fantasy creatures in the “Harry Potter” movies, who said he’s working to develop her books into a TV series, “The Saga of the Exiles.”

“I devoured them,” he said of the books. “The characters are wonderful, the sequencing is amazing, and the ideas behind the story are so bold.

He visited her at her home near Seattle and “discovered this lady who was a force of nature, passionately living life to the full in her 80s. You don’t meet many ladies of that age who head off in a truck to go fishing armed with a big stick in case she met bears.”

Julian May crafted stunning costumes for sci-fi conventions. | Family photo

Growing up near Grand and Harlem, she was known as Julia.

“She changed it to Julian at a very young age,” her son Alan Dikty said. “She preferred the sound of it.”

Her father was an engineer at a tool-and-die company and her mother a department manager for Montgomery Ward.

While in college at what’s now Dominican University, Ms. May sold her first sci-fi story — about aliens wielding balls of fire in an attack at the Indiana Dunes. “Dune Roller” appeared in “Astounding Science Fiction.” In the 1970s, it was made into a B-movie that played at drive-ins, “The Cremators.”

In 1951, she met Thaddeus Eugene Dikty — who would become her husband and a publisher of sci-fi and fantasy — at a science-fiction convention in Port Clinton, Ohio, according to their son.

In 1952, she chaired the 10th World Science Fiction Convention in Chicago, the first woman to do so.

She and her husband “had a lot of fun and went to a lot of other conventions,” Ms. May said in a 1982 interview with Pan Books. She said she sold one more sci-fi story “and then quit the field for 26 years.”

Sci-fi just didn’t pay in those days, she said. Ms. May worked for Encyclopedia Britannica and Follett publishing. In the late 1950s and the 1960s, she was a freelance writer who churned out Popular Mechanics books like “There’s Adventure in Marine Science” and “There’s Adventure in Jet Aircraft.”

Before returning to her first love — science-fiction and fantasy — Julian May churned out sports biographies for young adults.

In the 1970s, Ms. May turned out sports biographies including “Muhammad Ali, Boxing Superstar” and “Jim Brown Runs with the Ball.”

“I write for money and make no bones about it,” she told Pan Books.

She and her husband raised their three children in Hyde Park and Naperville. In the early ’70s, the couple moved to the Northwest, to the Portland area.

A mid-1970s trip to a sci-fi convention flipped a switch for her. “Deep inside my giant brain,” she told Pan Books, “the fantastic streak that had lain [dormant] for all those years erupted.”

In 1981, she published her first major book, “The Many-Colored Land.”

Filled with wordplay and allusions to ancient epics, her writing features “intelligent, flawed characters facing profound emotional dilemmas and genuine sacrifices,” said Dublin-based writer and radio producer Gareth Stack. “The scope, ambition and sheer scale of both her major series would require a visual treatment that would dwarf ‘Game of Thrones’ in scale.”

Said her son, “As she quite cheerfully told me, ‘What distinguishes my books is heavy doses of history, religion and sex.’ ”

Her final series, the “Boreal Moon” trilogy, was published about a decade ago.

Ms. May is also survived by her daughter Barbara and son David; sister Joan May Elias and brothers Robert and Daniel. Her family said her ashes have been scattered in the Washington state wilderness.

Julian May and her husband T.E. Dikty were members of the Society for Creative Anachronism. Here, she’s dressed as a medieval English gentlewoman and he as a Polish lord. | Family photo