Jennell Jaquays, who made luminous fantasy paintings, classic adventures for tabletop role-playing games like Dungeons & Dragons, and distinctive levels in popular video games like Quake II, died on Jan. 10 in Dallas. She was 67.

Ms. Jaquays’s wife, Rebecca Heineman, said she died in a hospital from complications of Guillain-Barré syndrome.

During Ms. Jaquays’s lengthy career, gaming grew from a niche hobby into a cultural touchstone. But long before Dungeons & Dragons was adapted into hit video games like “Baldur’s Gate 3” and films like “Dungeons & Dragons: Honor Among Thieves,” and before it served as a signifier of nerdiness on television shows like “Stranger Things,” “The Big Bang Theory” and “The Simpsons,” devotees shared the adventures they created with other hobbyists.

Ms. Jaquays (pronounced “JAY-quays”) discovered Dungeons & Dragons, often abbreviated as D&D, shortly after it was released in the mid-1970s, when she was studying art in college.

In D&D, a group of players create characters who go on an adventure run by a dungeon master. The outcomes of attacks and other actions are often decided by rolling many-sided dice.

The rules and background lore can take up entire tomes. Art like Ms. Jaquays’s promises excitement belied by the dense text of a game guide, and makes it far easier for players to envision creatures like Beholders (imagine a large, nasty, levitating meatball with a toothy maw, a colossal central eye, and many smaller eyes on swiveling stalks).

An artist can “show so much more in a 3-by-4-inch picture on a page than the designer can do in two pages of description,” Ms. Jaquays said in the documentary “Eye of the Beholder: The Art of Dungeons & Dragons” (2019).

Over nearly five decades, Ms. Jaquays illustrated the covers and interiors of settings, modules, books and magazines for D&D and other role-playing games. In one of them, a red dragon roars while perched in front of a snow-capped mountain; in another, a nautiluslike spaceship floats above an alien world; in a third, two Ghostbusters prepare to tangle with a field of animated jack-o’-lanterns.

Ms. Jaquays also crafted scenarios of her own. Two of her earliest D&D modules, “Dark Tower” and “The Caverns of Thracia,” are renowned for their pathbreaking designs.

In the early days of D&D, many scenarios were fairly linear — enter dungeon, defeat monsters and plunder, assuming your characters survive.

Ms. Jaquays’s adventures were not so straightforward. They often contained several possible entrances and multiple avenues, some of them secret, by which players could accomplish their goals.

“The result is a fantastically complex and dynamic environment: You can literally run dozens of groups through this module and every one of them will have a fresh and unique experience,” the game designer Justin Alexander wrote about dungeons like Ms. Jaquays’s on his website in 2010.

“Dark Tower” and “The Caverns of Thracia” are still available, and still being played, generations after Ms. Jaquays made them. Her name has also become a verb — “Jaquaysing the dungeon” means creating a scenario with myriad paths.

In the early 1980s Ms. Jaquays went to work for Coleco, and she eventually oversaw the teams that designed games for the Coleco Vision, an early home video game console; one notable project was “WarGames,” an adaptation of the 1983 film.

Long after leaving Coleco, when video games were vastly more sophisticated, Ms. Jaquays designed levels for the first-person shooters Quake II and III and the military strategy game Halo Wars. She also made The War Chiefs, an expansion pack that let users play as Native American cultures vying for power against European civilizations in Age of Empires III.

Jennell Allyn Jaquays was born on Oct. 14, 1956, in Michigan, and grew up in Spring Arbor, Mich., and Indiana. Her father, William, sold mobile classrooms; her mother, Janet (Lake) Jaquays, worked for a credit union.

After graduating from high school in 1974, she studied art at Spring Arbor University. Her brother introduced her to D&D in 1975.

Ms. Jaquays eventually worked with gaming friends to produce The Dungeoneer, a fanzine of D&D content for which she secured permission from TSR, the company that published the game.

The Dungeoneer developed a following, and Ms. Jaquays, who earned a bachelor’s degree in fine arts in 1978 and needed a more secure profession, sold the magazine and worked as an artist and game designer. She married Ruta Vaclavik in the late 1970s.

Ms. Jaquays got a job at Coleco a few years later, but she was laid off in the mid-1980s after a downturn in the video game industry. She spent years doing freelance art and design work for RPG publishers before she began working for TSR full time in the 1990s.

In 1997 Ms. Jaquays joined id Software, the company that made groundbreaking first-person shooters like Doom and Quake.

But building games with a small team in what Ms. Jaquays described as a sometimes toxic environment burned her out. She left id in 2002, the same year she divorced her first wife. A later marriage also ended in divorce.

Ms. Jaquays said in an interview posted on Medium in 2020 that she was in her mid-50s when she “finally accepted that I was transgender and that I could do something about it.”

She added, “It took two marriages and two divorces and my kids finally being established in their own lives for me to finally have the courage to confront my truth.”

Ms. Jaquays knew Ms. Heineman through gaming, and Ms. Heineman, a video game designer and advocate for transgender rights, helped Ms. Jaquays navigate her transition. Ms. Jaquays also became a transgender activist who served for a time as the creative director of the Transgender Human Rights Institute in Seattle.

Ms. Jaquays and Ms. Heineman married in 2013 and lived together in Heath, Texas. In addition to her wife, Ms. Jaquays is survived by a son, Zach, a video game designer with Bungee, and a daughter, Amanda Jaquays, from her first marriage; a brother, Bruce; a sister, Jolene Jaquays; three stepchildren, Maria, William and Cynthia Heineman; and four grandchildren.

After leaving id Ms. Jaquays worked full time for the video game studios CCP Games and Ensemble Studios. She also helped create a master’s degree program for video game design called Guildhall at Southern Methodist University in Dallas.

In recent years Ms. Jaquays focused on one huge project: “Central Casting,” a collection of elaborate back-story tables that allowed players to create character backgrounds by rolling dice.

She published the first of three “Central Casting” volumes in 1988, but it is out of print. She was almost done with “Central Casting” when she died, and Ms. Heineman said she was determined to get it into players’ hands.

“I’m going to make certain that wish is fulfilled,” she said.