Otto, Prince of Bismarck, Count of Bismarck-Schönhausen, Duke of Lauenburg (German: Otto Fürst von Bismarck, Graf von Bismarck-Schönhausen, Herzog zu Lauenburg, pronounced [ˈɔtoː fɔn ˈbɪsmaʁk] (listen); 1 April 1815 – 30 July 1898), born Otto Eduard Leopold von Bismarck, was a Prussian and later German statesman and diplomat. From his origins in the upper class of Junker landowners, Bismarck rose rapidly in Prussian politics, and from 1862 to 1890 he was the minister president and foreign minister of Prussia. Before his rise to the executive, he was the Prussian ambassador to Russia and France and served in both houses of the Prussian parliament. He masterminded the unification of Germany in 1871 and served as the first chancellor of the German Empire until 1890, in which capacity he dominated European affairs. He had served as chancellor of the North German Confederation from 1867 to 1871, alongside his responsibilities in the Kingdom of Prussia. He cooperated with King Wilhelm I of Prussia to unify the various German states, a partnership that would last for the rest of Wilhelm's life. The King granted Bismarck the titles of Count of Bismarck-Schönhausen in 1865 and Prince of Bismarck in 1871. Bismarck provoked three short, decisive wars against Denmark, Austria, and France. Following the victory against Austria, he abolished the supranational German Confederation and instead formed the North German Confederation as the first German national state, aligning the smaller North German states behind Prussia, while excluding Austria. Receiving the support of the independent South German states in the Confederation's defeat of France, he formed the German Empire – which also excluded Austria – and united Germany.

With Prussian dominance accomplished by 1871, Bismarck skillfully used balance of power diplomacy to maintain Germany's position in a peaceful Europe. To historian Eric Hobsbawm, Bismarck "remained undisputed world champion at the game of multilateral diplomatic chess for almost twenty years after 1871, [and] devoted himself exclusively, and successfully, to maintaining peace between the powers". However, the annexation of Alsace–Lorraine gave new fuel to French revanchism and Germanophobia. Bismarck's diplomacy of Realpolitik and powerful rule at home gained him the nickname the Iron Chancellor. German unification and rapid economic growth were foundational to his foreign policy. Juggling a very complex interlocking series of conferences, negotiations and alliances, he used his diplomatic skills to maintain Germany's position.

Bismarck disliked colonialism because he thought it would consume German resources rather than reaping the benefit of it but reluctantly built an overseas empire when it was demanded by both elite and mass opinion; Bismarck was also initially opposed to the German annexation of Alsace–Lorraine from France, as he thought, correctly, that it would engender long-term enmity among the French toward Germany.

A master of complex politics at home, Bismarck created the first welfare state in the modern world, with the goal of gaining working class support that might otherwise go to his socialist opponents. In the 1870s, he allied himself with the low-tariff, anti-Catholic Liberals and fought the Catholic Church in what was called the Kulturkampf ("culture struggle"). He lost this struggle, as the Catholics responded by forming the powerful German Centre Party and using universal male suffrage to gain a bloc of seats. Bismarck then reversed himself, ended the Kulturkampf, broke with the Liberals, imposed protective tariffs, and formed a political alliance with the Centre Party to fight the Socialists. A devout Lutheran, he was loyal to his ruler, German Emperor (Kaiser) Wilhelm I, who argued with Bismarck but in the end supported him against the advice of Wilhelm's wife and son. While the Imperial Reichstag was elected by universal male suffrage, it did not have much control of government policy. Bismarck distrusted democracy and ruled through a strong, well-trained bureaucracy with power in the hands of a traditional Junker elite that consisted of the landed nobility in eastern Prussia. In his role as chancellor, he largely controlled domestic and foreign affairs. In 1888, which came to be known as the Year of the Three Emperors, the German throne passed from Wilhelm I to his son Frederick III to Frederick's son Wilhelm II. The headstrong Kaiser Wilhelm II dismissed Bismarck from office, and Bismarck retired to write his memoirs.

Bismarck's legacy is best remembered for his indispensable role in German Unification. As head of both Prussia and later Germany, Bismarck possessed not only a long-term national and international vision but also the short-term ability to juggle complex developments. For this reason, he became a hero to German nationalists, who built many monuments honouring him. Historians praise him as a visionary who was instrumental in uniting Germany and, once that had been accomplished, kept the peace in Europe through adroit diplomacy. However he has been criticized for his domestic policies such as Catholic persecution, and the centralization of executive power, which some describe as Caesarist. Furthermore he has been criticized by opponents of German nationalism, as nationalism became engrained in German culture, galvanizing the country to aggressively pursue nationalistic policies in both World Wars.