The most prolific author in a survey of Western lit is not Shakespeare, a piker with less than forty plays; Georges Simenon, whose 84 Maigret novels were less than half of his corpus; or Isaac Asimov, with more than 250 books to his credit. Dame Barbara Cartland, who churned out over seven hundred books (largely interchangable romance novels) in her seventy-seven-year career as an author, is a serious contender, but in the Harvard libraries, Anonymous has got her beat. Being intentionally anonymous is different from being anonymous just because we don’t know who you are. The Pearl poet, among the greatest fourteenth-century English poets, is presumably unknown because we lack a great deal of historical evidence from the fourteenth-century. And using an obvious pseudonym like "John Doe" seems awfully similar to just going by "Anonymous"; pseudonyms that are not recognizable as pseudonyms aren’t quite the same. Whether Eric Blair (who may have wanted a name he could dispose of if his first book didn’t sell), C.L. Moore and Henry Kuttner (married pulp authors who used several pen names for their collaborative work), or Alice Sheldon (who didn’t want her largely male audience to dismiss her incindiary science fiction of the ‘60s and ‘70s because she was a woman) existed or not, one could imagine writers, real people with real lives, named George Orwell, Lewis Padgett, and James Tiptree, Jr. The same cannot be said for "Dakota North", a pen name used for a blue novel by an acquaintance of mine. One imagines Dakota getting out of bed in the middle of the night to type up something brilliant while his wife, Caroline, slumbers.
What is the rationale behind using an obvious pseudonym (or simply writing as "Anonymous")? Some might do it because the work is embarassing or would cause a conflict with their real-world identity. When Don Foster, textual investigator, identified the author of Primary Colors, Joe Klein‘s anonymous roman a clef, it stirred up a ruckus. Klein’s novel and his initial refusal to admit that he wrote it surely distracted the people his day job as a reporter required him to interact with. Sometimes it’s to avoid controversy (and perhaps hate mail). For political weblog folk like "Charles Musil" and "Charles Dodgson", it’s probably a combination of the above, along with a feeling that their identities when not eviscerating their political opponents are none of our business.
The pamphleteers of eighteenth-century America, Cato and Candidus might or might not have been in legal trouble for what they wrote, but they certainly displeased many, and anonymous pamphlets were the fashion of the day. But some people seem reject individual identity solely due to ideology or aesthetics. The French techno group Daft Punk wear visored motorcycle helmets at their performances. San Francisco rock band/conceptual art project/freakshow geniuses the Residents have built an entire mythology around their anonymity (including their trademark top-hatted eyeball masks; the Residents never show their faces in public). For Netochka Nezvanova ("Nameless Nobody", roughly; the name is from Dostoyevsky), it may be ideology, aesthetics, the occasional illegality of her behavior, a desire to cover her real age, nationality, or gender. Or it may simply be that Nezvanova, as a single entity, does not exist.
Dating back at least as far as Vernor Vinge’s prescient "True Names", science fiction has realized that on the Internet, no one knows you’re a dog. Dozens of books and probably hundreds of stories have dealt with the fluidity of identity (socio-economic, demographic, gender, and racial in both senses of the words) when persona is divorced from person. The real world is catching up, which means that the days (as promised by William Gibson and Warren Ellis) of computer-generated pop stars slavishly followed by millions cannot be far behind. On the successor to the Internet, science fiction tells us, everyone will know you’re a sophisticated computer-rendered actor with a set of focus-group-tested canned responses singing bad but catchy J-pop, and nobody will care.