Jonas Šliūpas (6 March 1861 – 6 November 1944) was a Lithuanian activist during the Lithuanian National Revival. For 35 years, he lived in the United States working to build national consciousness of Lithuanian Americans. He edited numerous periodicals, organized various societies, and published some 70 books and brochures on various topics. His sharp criticism of the Catholic Church made him highly controversial and unpopular among the conservative Lithuanians.

As a student at Mitau Gymnasium, Šliūpas read works by John William Draper that he later credited for laying the foundations for his lifelong dedication to freethought, promotion of science, and criticism of the Catholic Church. His studies at the Imperial Moscow University and Saint Petersburg Imperial University were cut short when was imprisoned for participating in a student riot in 1882. He fled to East Prussia where he edited Aušra, the first Lithuanian newspaper. He fled from the German police to United States in June 1884. Despite severe financial hardships, he began publishing Lithuanian newspapers Unija and Lietuviškasis balsas. Soon, Pennsylvania Lithuanians began publishing Vienybė lietuvninkų in response to Šliūpas' anti-Catholic and anti-Polish rhetoric. Šliūpas established the Lithuanian Scientific Society which was active until 1896. To secure means of making a decent living, Šliūpas studied medicine at the University of Maryland School of Medicine and started a successful private medical practice in 1891.

Šliūpas anti-religious and pro-socialist views grew stronger and louder. He published socialist weekly magazine Nauja gadynė (1894–1896), freethrought monthly magazine Laisvoji mintis (1910–1914), various mainly translated texts promoting freethought and publicizing the conflict thesis between Christianity and science, and texts on the history of Lithuania (including three-volume history of Lithuania in 1904–1909). He organized Lithuanian miners in response to the Lattimer massacre in September 1897 and during the Coal strike of 1902 and unsuccessfully ran in the elections to the United States House of Representatives in 1896 and 1900. He was a popular public speaker and by 1907 had given over 1,000 lectures on political, social, religious and scientific subjects. At the outbreak of World War I, Šliūpas organized the Lithuanian National League of America as the third or middle road between the radical socialists and the conservative Catholics. He organized fundraising drives to help Lithuanian war refugees, visited Russia in 1916–1918, and publicized the Lithuanian demands for independence in English-language essays and memorandums (one of them was added to the Congressional Record). In 1919, Šliūpas briefly represented Lithuania in London, at the Paris Peace Conference, and in Latvia.

While Šliūpas was respected for his past contributions to Lithuanian causes, he was not invited to the Lithuanian government or held a more prominent public position. Šliūpas returned to Lithuania in 1920 with substantial savings that he invested in the Trade and Industry Bank and other business ventures, many established by his son-in-law Martynas Yčas. Most of these investments were lost when the bank failed in 1927. He served as a mayor of Palanga (1933–1935, 1938–1939, 1941), a developing seaside resort, and had to coordinate the response to the great fire in May 1938 that left some 1,500 people homeless. He continued to promote freethinking – chaired Freethinkers' Society of Ethical Culture, edited reestablished Laisvoji mintis (1933–1940), lobbied for non-religious cemeteries, schools, marriage and birth registrations, published numerous anti-religious texts. He continued to be active in public life until his death. As many other Lithuanians, he fled from the advancing Red Army in October 1944 and died suddenly in Germany.

Biography Early life and education Šliūpas was born in a well-off family in near Gruzdžiai on . According to Šliūpas' memoirs, his family told stories about their wealthy ancestors who traced back to the time of Grand Duke Vytautas (died in 1430). His uncle Aloyzas attended Kražiai College and later became a priest. His father owned 36 dessiatins of land and decided to educated all three sons. In summer 1868, his uncle Aloyzas took Šliūpas to live with him in near Betygala and later in Pernau. There, Šliūpas studied Russian and Polish languages and witnessed moral degradation of the clergy, even his uncle who lived with his housekeeper in sin and somehow managed to obtain large sums of money. He was beaten for various infractions and after a year and a half begged his parents to take him home. He was taken in by an uncle on his mother's side who educated him to pass the entrance examinations to a gymnasium. In 1871, he failed the Russian language exam at the Šiauliai Gymnasium. A year later, he passed the exams at the but was not admitted due to lack of vacancies. While visiting Kaunas, Šliūpas received confirmation from bishop Motiejus Valančius.

Finally, Šliūpas was admitted to a preparatory class of the Mitau Gymnasium (present-day Latvia). He exhibited academic aptitude and, after finishing the preparatory class and taking exams, he was admitted to the 2nd class of the gymnasium in 1873 therefore skipping the 1st class. He continued to excel at his studies and received tuition waivers. He received financial support from his uncle and earned additional money by tutoring. For example, he spent the summer 1879 teaching noble children in a manor in Pandėlys. Though the gymnasium had only a few Lithuanian students and no Lithuanian societies, Šliūpas began developing his interest in the Lithuanian language, history, and culture. He read historical works by Józef Ignacy Kraszewski, began writing Lithuanian texts (translations of texts by E. T. A. Hoffmann and Thomas Mayne Reid), subscribed to Lithuanian newspaper Keleivis published in Königsberg, became a member of the Lithuanian Literary Society and contributed Lithuanian folktales to its publications. He also read Polish translations of History of the Intellectual Development of Europe and History of the Conflict Between Religion and Science by John William Draper which Šliūpas credited in his memoirs for laying the foundations for his lifelong dedication to freethought. He graduated the gymnasium with top grades in 1880 and continued studies at the Imperial Moscow University.

In Moscow, Šliūpas initially studied philology, but after one semester transferred to law. His good grades earned him tuition waivers. He met a small group of Lithuanian students who soon organized a Lithuanian society which published hectographed irregular Lithuanian newspaper Aušra (Dawn). In his memoirs, linguist Jonas Jablonskis claimed that this group inspired him to begin working for the Lithuanian causes. He also became interested in socialism, establishing contacts with and Count Vladimir Zubov. Together with Janavičius, Šliūpas spent summer 1881 visiting various locations across Lithuania collecting funds to support members of revolutionary groups Narodnaya Volya and Black Repartition suffering from political repressions. In Moscow, he visited the Rumyantsev Museum, attended meetings of the Russian Geographical Society, listened to debates between professors Dmitry Ilovaysky and on the origins of Slavs. He corresponded with linguists Filipp Fortunatov and Vatroslav Jagić writing to them not in Russian, but in Lithuanian. In summer 1882, Šliūpas visited East Prussia to investigate the possibility of publishing a Lithuanian-language periodical – the printing of Lithuanian texts in the Latin alphabet was banned in the Russian Empire since 1864. He stopped in Kaunas and stayed with priest Antanas Baranauskas while he copied a manuscript by Simonas Daukantas on the history of Lithuania which was kept at the library of the Kaunas Priest Seminary. In Prussia, he met with members of the Lithuanian Literary Society in Tilsit (now Sovetsk), Lithuanian publisher Martynas Jankus in Ragnit (now Neman), and editor of Lietuwißka Ceitunga in Memel (now Klaipėda). Back in Lithuania, Šliūpas stopped in Žagarė to visit priest Ignotas Vaišvila to collect biographical information about Daukantas who lived with Vaišvila in his last years.

In fall 1882, Šliūpas transferred to Saint Petersburg Imperial University to study natural science. At the same time, hoping that the new Tsar Alexander III of Russia would lift the Lithuanian press ban, he prepared a Lithuanian calendar and submitted it to Russian censors. He also sent a petition, dated 7 November 1882, to the Ministry of Internal Affairs asking to lift the ban. Both requests were denied. He also worked to publish hectographed socialist manifestos and proclamations. His studies were cut short when he was implicated in a student riot, arrested, and imprisoned in the Kresty Prison for three months. He became ill and the police allowed him to return to his native Rakandžiai. There he wrote a biography of Simonas Daukantas (published in Aušra) and a socialist work on social inequality (attempted to publish in Geneva, but unfinished due to lack of funds; a copy was later kept by Vincas Kapsukas). In spring 1883, he was invited by count Nikolay Zubov to teach at his manor in . He applied to different Russian universities in Kiev, Kazan, Kharkiv, Tartu, but was not admitted due to his prior arrest. Faced with conscription to the Imperial Russian Army, Šliūpas decided to flee abroad.

Editor of Aušra In fall 1883, Šliūpas decided to leave to Geneva, Switzerland, which was a refuge for many Russian and Polish socialists. He had promises of financial support from Janavičius and Zubov as well as lofty hopes of establishing a Lithuanian press for socialist publications. He also wanted to finish his studies at the University of Geneva. Šliūpas established contacts with Polish socialist Bolesław Limanowski, began publishing his own socialist brochure, and wrote another brochure Išganymas vargdienio (The Salvation of a Pauper) in which he was the first to raise the idea of independent (not merely autonomous) Lithuania. The brochure was later published in Unija and as a separate booklet in the United States. Šliūpas did not receive the promised financial support from Lithuania. Searching for means of living, he rejected an invitation to join Narodnaya Volya and was about to emigrate to Chile to become a farmer, but received an offer from Martynas Jankus to become the editor of Aušra, the first Lithuanian-language newspaper published in Ragnit (now Neman) in East Prussia. On his way to Bitėnai, Šliūpas met with Jonas Basanavičius, who previously had editorial control of Aušra and who at the time lived in Prague. Basanavičius wanted Šliūpas to send all texts of Aušra for his final approval, but that was impractical. Basanavičius envisioned Aušra as a historical and literary periodical which would showcase the greatness of Lithuania's history, raise Lithuanian national consciousness, and promote education as means to lift oneself from poverty and oppression – i.e. promote romantic nationalism with careful additions of freethought not to alienate the majority Catholic population. In five months, Šliūpas edited twelve issues of Aušra. He introduced some socialist themes to Aušra – articles promoting economic development with the ultimate goal of social equality, descriptions of poor conditions of peasants and manor workers, etc. This socialist tinge was enough to alienate the Catholic clergy who started treating Aušra with suspicion if not outright hostility.