Complex sentence: He began as one of the most promising of British post-war poets, but became more famous as a critic, writing biographies of Robert Graves (whom he met first at age 14), Rudyard Kipling and Thomas Hardy, and producing numerous critical studies.
Split into simpler sentences: He began as one of the most promising of British post-war poets. However, he became more famous as a critic, writing biographies of Robert Graves (whom he met first at age 14), Rudyard Kipling and Thomas Hardy, and producing numerous critical studies.