Mr. Turner died June 27 at a Santa Monica hospital of complications related to cancer, said Vince Hernandez, editor in chief of Aspen MLT, the Santa Monica publishing company Mr. Turner founded in 2003. Through his company, Mr. Turner created online comic adaptations for the NBC series "Heroes" and published his own titles, including the best-selling Fathom, a deep-sea story about a female superhero with water-based powers.

"He was definitely one of the most popular and influential comic-book artists working right now," said Andrew Farago, curator of San Francisco's Cartoon Art Museum. "He was very, very much in demand as a cover artist on high-profile projects." Since 2000, Mr. Turner had battled chondrosarcoma, a bone cancer. The illness hindered his ability to do the labor-intensive sequential art required of comic-book storytelling and was one reason he turned to drawing covers.

He was a bankable name whose ethereal yet dynamic cover art often boosted sales. Ryan Liebowitz, general manager of the Golden Apple Comics store in Los Angeles, said Mr. Turner's name was synonymous with special-edition covers that often became collectibles. "He was doing just the covers for the biggest and best projects -- Justice League for DC or Civil War for Marvel," Liebowitz said. "Fans would clamor for that."