David Emmett Cockrum was born in Pendleton, Oregon, on November 12, 1943. He grew up loving comic books with the ambition to become a comic-book creator himself, and later become a professional comic book illustrator who in the mid-1970s helped invent a dynamic new look and intriguing new characters for the moribund “X-Men” comics, paving the way for what became America’s most popular comic books and a billion-dollar movie empire.

Following his school graduation, Cockrum joined the United States Navy for six years. After his discharge in the early 1970s, Mr. Cockrum moved to New York, where he worked as an inker, who refines the art of the original artist, called a penciller. He did this for Murphy Anderson, who created the modern look of Superman, Batman, Flash and other characters at DC Comics. Clifford Meth, who has written extensively about comic-book art, said Mr. Cockrum created a new look for superheroes, featuring wide shoulder lapels, big belts and buccaneer boots.

DC made him the first artist, or penciller, in redefining the DC team the Legion of Super-Heroes. His costumes and style for the group persisted into the 1980s. After a dispute with DC, Mr. Cockrum moved to its arch-competitor, Marvel. Though the company contended it owed him nothing because he worked as freelancer, it paid him $200,000 and royalties for one character, Nightcrawler, his earliest, according to The Comics Journal. The terms were not officially revealed. While not confirming or denying the $200,000 figure, Mr. Adams said Mr. Cockrum deserved more. “They took his characters and made an industry out of them,” he said.

He worked less often as his health deteriorated, and died due to complications from diabetes.