(Where would this world be without Mark Twain (a nym for Samuel Clemmens), Maxwell Grant (the nym for Walter B. Gibson and others for the Shadow pulps), and the thousands of other nyms that appear in the publishing field?)
Heinlein used a few nyms. His best stories were published under the names Robert Heinlein and Anson Macdonald. The Heinlein/Macdonald split came about because John W. Campbell didn't want it to look like _Astounding_ was being dominated by one other, though the quailty of the stories was about the same. (All but a couple of dthe Future History stories were published under one of these names, but I don't remember which). Heinlein used other nyms for stories of lesser quailty, or stories he sold to other markets in genres other than sf. He created one nym to sell off stories that he described as "stinkeroos", and went so far as to get a separate PO Box in the name of this nym so that it couldn't be associated with Robert Heinlein. Ken