Everybody who follows comic books (or at least did so in the 1980s) knows about the X-Men, and everybody who knew the X-Men knew Chris Claremont. From 1975 until 1991, he was the writer for the lives of the most unusual and, eventually, the most popular team of superheroes comicdom had ever seen. In 1999 he found his way back into that series, as well as additional editorial responsibilites at Marvel Comics. Some fans love him, some hate him, and some have moved on without him. But it's those sixteen straight years with one team which still characterize him and make him worth respecting.
Apparently, Claremont had been working at Marvel's offices in the 1960s as a gofer for some time before getting paid for his writing. His first known creative credit, it so happens, was for an X-Men issue someone else was writing:
"...Roy [Thomas] was wrapping up the Sentinels story, and we were talking in the ofice one day, just in general terms. He was looking for a rationale to get rid of the Sentinels. As I recall he didn't think the X-Men could defeat them. There were too many of them and they were too powerful. What he wanted Scott to do was to outwit them, or to use their own logic against them. He wanted him to find some key that could be utilized to that end. With my typically dilettantish and probably inaccurate view of science and generic theories, it seemed to so as I understood it, all primary mutation was the result of solar radiation. Just the gradual seepage of it through the Van Allen belts. The only way to stop unwanted mutation was to destroy the sun. The Sentinels would be arrogant enough to try and stupid enough not to realize that it would cook their goose. They evidently had no self-survival program. "Let's go to the sun!" Zoop! It seemed like a good idea to Roy so he incorporated it into the story." (From an interview with Chris Claremont in The X-Men Companion I, edited by Peter Sanderson, Fantagraphic Books, March 1982, p. 90.)
He chipped in here and there on different comics, but his first publication of his own was actually a short prose story for the Magazine of Fantasy and Science Fiction. Soon after that he got five pages of prose in Marvel's Dracula Lives! publication, a story imaginatively titled "Who Is Bram Stoker and Why Is He Saying Those Terrible Things About Me?" and later that year his first comic story was published in Daredevil, issue #102.
More prose and book reviews followed, but Marvel was all about comic books, after all, and he couldn't avoid them forever. He scripted and wrote for War is Hell starting in 1974 and did other creative and editorial work until the creators of Marvel's upcoming Giant-Size X-Men #1 were overheard trying to work out a plot problem: how to end the issue. At this time, The X-Men has been in reprints for years and Marvel was making a concentrated effort to revive the title with an "all-new, all different" team from around the globe. Claremont contributed a little bit of pseudoscience to that story as well (something about using the characters' powers over magnetism to neutralize their opponent's gravitational hold on the Earth), and the writer was grateful and used it in the story.
When the new X-Men took off, X-Men #94 was the first monthly issue with the new team, and Claremont contributed a script to it. #95 too. Issue #96 was all his, and so were the ones following. He was scripting and writing all over the place, as Marvel's writers were wont to do, but over the years the X-Men became more and more popular and Claremont's attentions were allowed to focus more and more on those characters.
Then came the crossovers. Early 1982 saw the arrival of Marvel Fanfare, a short-lived series which featured both the X-Men and other popular Marvel characters. Later that year came fan-favorite Wolverine's own four-issue limited series, which was timed to cross over neatly with events in The Uncanny X-Men. (Claremont was also writing monthly for Spider-Woman at this time.) Then the New Mutants arrived, in a graphic novel which was followed by an ongoing monthly series. While writing for both that title and Uncanny X-Men, he contributed additional limited series, but always involving the X-Men characters which were now, unquestionably, his own. In 1984 he published a multipart story in Marvel's creator-focused Epic Illustrated magazine; it would be his last non-X story for some time.
Nobody seemed to complain, though. Claremont was more familiar with "his" X-Men than anyone else, and he just kept turning out ideas which no one else would have dared to try. What fans most admired was his willingness to keep things a little edgy, both the characters and events. In 1980 he wrote the now-legendary Dark Phoenix saga, which ended with Phoenix, a major character and longtime love interest of team leader Cyclops, being overwhelmed by her own potential for destruction and finally destroying herself before she got any more out of control. This story and others like it were exactly what catapulted the X-Men to the top of the sales charts, a position those characters continued to hold for years with or without Claremont's writing. The eventual decision, years later, to bring Phoenix back to the X-Men universe sans powers was one that was beyond Claremont's control. (He's still a little bitter about it.)
By the 1990s, partly because of editorial moves like that one and partly because the popularity of certain comic book artists was leading them to think they could do the writers' job better on their own, Claremont was looking for creative outlets that didn't have an "X" written on them. A three-issue story for Marvel's second X-Men monthly was his last, and his quest for independence began. His first solo novel, FirstFlight, was part of a science fiction trilogy about astronaut-pilots which was tepidly received by readers. In 1995 another trilogy of fantasy novels based on George Lucas' movie Willow was released; fans accused it of being too slow and boring to keep up with. He contributed work to the Star Trek comics published by Marvel's rival, DC Comics, as well as to smaller publishers like Dark Horse, Image, and Defiant, and eventually created his own superhero team for DC entitled Sovereign Seven.
This book became his primary focus until 1997, when Marvel enlisted him to help complete their Heroes Reborn crossover limited series and, immediately following, write for one of their mainstay titles, the Fantastic Four. Sovereign Seven finally fizzled out in mid-1998 after only three years, when it became painfully clear that fans were more interested in seeing other writers tell the stories of the X-Men than in seeing Claremont tell the stories of other characters. Whether it was conditional on his return to writing or not, Claremont was given a position on Marvel's editorial staff as well, a position he holds to this day.
Claremont contributed a few issues to Wolverine again that year, but Fantastic Four was his main project until Marvel pulled him back to the X-Men titles in 1999 -- coincidentally, for uncredited script work on the new X-Men #95. He did double duty on Fantastic Four and Uncanny X-Men until Fantastic Four #32 in mid-2000, when he began doing double-duty on both X-Men monthlies again. Plus the occasional limited series.
Claremont's trademarks have always been his fully three-dimensional characters (if they don't have a few flaws and a lot of motivation, he just doesn't keep them around), attention to detail (Claremont's worst pseudoscience was and is far more believable than was most comic book writers would ever cobble together), and inordinately wordy dialogue and narrations (future writers, including Claremont himself, would periodically poke fun at just how much his characters could expound on their motivations in mid-leap). Certain phrases used and re-used by his X-Men characters became "Claremontisms" which fans could identify anywhere -- his uncredited work on X-Men #95 was recognized a mile away by the fan community.
Today he holds the twin titles of vice president and editorial director at Marvel Comics, as well as writing for both X-Men titles. He misses the freedom he had back when Marvel was a smaller company with fewer editors and fewer X-Men-related titles, not to mention the "lost years" when he gave the X-Men over to other writers. But those characters were and are -- for better or for worse -- what he does best.
Sources: http://www.chrisclaremontchecklist.org,
assorted interviews, and my own years of exposure
to his work and fans