European comicbook publishers had been doing it for decades, but it wasn't until the early 1980s that the "graphic novel format" (8.5 x 11 full-process color comics of varying page lengths--usually a minimum of 48 pages--on glossy paper with cardstock covers--though some "extra special" gns were published in hardcover and often later reprinted with the standard cardstock covers) came into vogue. Eclipse had tried it in the late 70s with Sabre, and even Marvel gave it a shot with the 1978 Stan Lee/Jack Kirby Silver Surfer reunion. Never mind the fact that the term "graphic novel" meant a lot of different things back in the early 80s. To some it meant Dave Sim's plans to do his Cerebus comic as a 300 issue story with a beginning, middle, and end. To others it meant the done-in-one, 100 or so page, single issue stories like Steranko's Chandler being published in Byron Priess' Fiction Illustrated. There was also a camp that believed the term belonged to collections of serialized stories, like Will Eisner's A Contract With God. There were (and still are) debates about what the term "graphic novel" really means, but Marvel and DC really muddied the waters when they applied the term as the title to their lines of European-style comics.
In 1982, Marvel initiated their line of European-style comics with Marvel Graphic Novel #1, featuring "The Death of Captain Marvel" by Jim Starlin. Why Marvel felt the need to number their "graphic novels" I'll never know. Each gn was a one-shot with no ties to past or future gn's. Perhaps they were toying with the notorious "collector's mentality" so many of us fans are saddled with. Still, they officially stopped numbering them with MGN #20, though many sources insist on numbering the first 38 or 39 gns, irregardless. Publishing "graphic novels" was really taking a chance, financially, considering their prices ranged from $4.95 to $7.95 in a time when comicbooks prices ranged from sixty to seventy-five cents. Still, the packaging was enticing, the concepts were often intriguing, and the talent working on them was usually top-notch, at least in the early days. For example, the second issue reprinted "Elric: The Dreaming City" (reprinted from early issues of Epic Illustrated) by Roy Thomas and P. Craig Russell; issue 3 was all-Starlin again with "Dreadstar" (a spin-off of his "Metamorphosis Odyssey" series from--
you guessed it--Epic Illustrated) which led to a Dreadstar series under Marvel's Epic imprint; issue #4 gave us the debut of Chris Claremont and Bob McCleod's New Mutants, serving as an introduction to Marvel's upcoming New Mutants comicbook; #5 featured the X-Men in the acclaimed "God Loves, Man Kills" by Claremont and Brent Anderson; #6 starred Walt Simonson's Star Slammers; #7 allowed Don McGregor and P. Craig Russell to "complete" their Killraven saga (from the War of the Worlds series in the 1970s Amazing Adventures)...and on it went. Some of the gns were purely hyped-up, expensive (if extremely well done) previews of upcoming comics (Dreadstar, New Mutants, Futerians, Void Indigo, Starstruck, and Swords of the Swashbucklers). Others featured Marvel characters in stories too big, violent, and/or sexy for their regular Comics Code approved mags ("Death of Captain Marvel", "God Loves, Man Kills", "Revenge of the Living Monolith", "The Sensational She-Hulk" (by John Byrne), "Shamballa", "Daredevil" (by Frank Miller and Bill Sienkiewicz), "Emperor Doom", "The Incredible Hulk and the Thing" (by Starlin and Bernie Wrightson), et al. 
A few were just a chance for top creators to experiment and do something they really wanted to do (Star Slammers, "Super-Boxers", "Spider-Man: Hooky"). And some--well, some were just a waste of time and could just have easily have been published as regular comicbook annuals ("Dazzler: The Movie", "The Aladdin Effect", "Thor: I Whom the Gods Would Destroy"). Eventually, Marvel would even give their Epic line of comics their own "graphic novel" series. With or without numbering, Marvel's "graphic novel" line hung around for just over a decade, providing fans with some good ("Silver Surfer: Judgement Day"), some bad ("Wolfpack"), and some just plain ugly ("Heartburst").
DC got into publishing "graphic novels" with a tentative step in 1981, when they created a new Superman story for their German markets and decided to produce it in English to see how it would sell in the newly-borning comics shops. Superman Spectacular #1 is a hard-to-find item, now, but it got the ball rolling. In 1983, DC got into publishing "graphic novels" with a bit more gusto, producing it's own line of gns with the very original umbrella title of DC Graphic Novel. DC's approach, however, was quite different from Marvel's. With rare exception, DC's gns were one-shot stories set outside the DC Universe. They were strictly sci-fi and fantasy comics like "Star Raiders", "Warlords", and "Metalzoic". In its short, seven issue run (August 1983-August 1986), the only time DC Graphic Novel ran a DCU-centric story was when they allowed Jack Kirby to wrap-up his New Gods/Fourth World saga with "The Hunger Dogs". 
From 1985-1987, DC tried it again, this time adapting famous science fiction stories by the likes of Harlan Ellison, Robert Silverberg, Robert Bloch, Ray Bradbury, Frederick Pohl, Larry Niven, and George R. R. Martin. The uninspiringly titled DC Science Fiction Graphic Novel line, edited by the Grand Master Julie Schwartz, himself, produced seven beautifully-illustrated issues (Gene Colan, Marshall Rogers, and others produced the art) before biting the dust. After that, from 1987 through the early 90s, DC's "graphic novel" energies were spent mostly on Batman, starting with the classic "Son of the Demon" (by Mike W. Barr and Jerry Bingham) and including "Batman: Digital Justice" (created completely on computer by Pepe Moreno), "Night Cries", and others.
First Comics also got into the "graphic novel" game in 1984 with their First Graphic Novel series (the lack of original titles must have been a prerequisite for publishing gns) featuring Beowulf, Nexus, Eric Shanower's Oz series, American Flagg, Elric, and many others. Much like Marvel's GN series, First Graphic Novels featured series tie-ins, previews, one-shots by hot creators, and reprints.
Many other publishers tried their hands at "graphic novels" in the 80s, especially the company that pretty much pioneered the format (in the U.S.), Eclipse Comics. Besides Sabre, they published many original gns and collections like Jim Starlin's The Price (also part of the "Metamorphosis Odyssey" series) and Dave Stevens' Rocketeer.By the mid-80s, publishers were transitioning over to a couple variations on the European format: the "prestige" comic, which was exactly the same format as the "graphic novel" except its size was the same as a standard comicbook and the trade paperback, which is the same, popular format we have today for collecting four or more issues of standard comicbook stories. Those two formats eventually rooted the "graphic novel" format off the shelves, until the trade paperback emerged supreme in the 1990s.
