So, some authors come to be known by a single book, or a single series within a larger body of work. Out of the many things he or she wrote, this one work comes to be the defining legacy.*
Some writers are fine with that. They're happy to be remembered, and it doesn't bother them that they're remembered for Book A as opposed to Book B. I think P. G. Wodehouse was one of these. Far from being annoyed that people wanted more Jeeves and Bertie Wooster stories from him year after year, he seems to have felt himself jolly lucky that readers still wanted more, and he was happy to oblige.** Tolkien belonged to this category: when asked in an interview how he wanted to be remembered, he replied that he hadn't much choice in the matter: that if he was remembered at all it'd be for LORD OF THE RINGS.***
Other authors, while grateful for the popularity a successful work brings, come to feel resentment over time for being treated like a one-hit wonder. A prime example of this is Sir Arthur Conan Doyle, whose Sherlock Holmes stories overshadow anything else he ever wrote, and rightly so -- and it was already apparent from early on in Doyle's career that this wd be the case.****
It was A. A. Milne's misfortune that he had a bad case of Conan Doyle disease. He wanted to be remembered as a witty and popular playwright; a persuasive advocate of pacifism (when pacifism was popular) and then stern critic of pacifist (when there was an actual war going on); a bold critic of Xianity.; a serious modern novelist Instead, he's remembered for Winnie-the-Pooh. Milne was already popular: the Pooh books made him famous. He was already making a more-than-comfortable living as a playwright; Pooh & company made him rich (and he enthusiastically encouraged merchandising of the same from v. early on). But he found it hard to be thought of as just a children's author, and growing harder as the years passed: not a Noel Coward but a second James Barrie.
current reading: Thwaite on Milne (1990)
current music: THE ENDLESS RIVER (2014; the last Pink Floyd album)
*thanks to Paul W. having queried this usage in a comment on an earlier post.
**the first Bertie & Jeeves story having been published in 1914 and the last in 1974, when the author was in his nineties.
***as opposed to his scholarly pieces, which he characterized as 'small', unimportant by comparison.
****A more modern example wd be Gary Gygax, who will always be remembered as the man who wrote D&D (esp. the three volume AD&D rules set), not by any of the games he turned out in the final twenty years of his career