Background: Vladimir Vladimirovich Nabokov (; Russian: Vladimir Vladimirovich Nabokov, pronounced [vla'djimjIr na'bok@f] ( listen), also known by the pen name Vladimir Sirin; 22 April [O.S. 10 April] 1899 - 2 July 1977) was a Russian-American novelist, translator and entomologist.
Context: The Nabokovs settled in Manhattan and Vladimir began volunteer work as an entomologist at the American Museum of Natural History.  Nabokov joined the staff of Wellesley College in 1941 as resident lecturer in comparative literature. The position, created specifically for him, provided an income and free time to write creatively and pursue his lepidoptery. Nabokov is remembered as the founder of Wellesley's Russian Department. The Nabokovs resided in Wellesley, Massachusetts, during the 1941-42 academic year. In September 1942 they moved to Cambridge where they lived until June 1948. Following a lecture tour through the United States, Nabokov returned to Wellesley for the 1944-45 academic year as a lecturer in Russian. In 1945, he became a naturalized citizen of the United States. He served through the 1947-48 term as Wellesley's one-man Russian Department, offering courses in Russian language and literature. His classes were popular, due as much to his unique teaching style as to the wartime interest in all things Russian. At the same time he was the de facto curator of lepidoptery at Harvard University's Museum of Comparative Zoology. After being encouraged by Morris Bishop, Nabokov left Wellesley in 1948 to teach Russian and European literature at Cornell University, where he taught until 1959. Among his students at Cornell was future U.S. Supreme Court Justice Ruth Bader Ginsburg, who later identified Nabokov as a major influence on her development as a writer.  Nabokov wrote Lolita while travelling on butterfly-collection trips in the western United States that he undertook every summer. Vera acted as "secretary, typist, editor, proofreader, translator and bibliographer; his agent, business manager, legal counsel and chauffeur; his research assistant, teaching assistant and professorial understudy"; when Nabokov attempted to burn unfinished drafts of Lolita, it was Vera who stopped him. He called her the best-humored woman he had ever known.  In June 1953 Nabokov and his family went to Ashland, Oregon. There he finished Lolita and began writing the novel Pnin. He roamed the nearby mountains looking for butterflies, and wrote a poem called Lines Written in Oregon. On 1 October 1953, he and his family returned to Ithaca, New York, where he would later teach the young writer Thomas Pynchon.
Question: what was his biggest achievment?

Answer:
Oregon. There he finished Lolita and began writing the novel Pnin. He roamed the nearby mountains looking for butterflies,