Józef Zachariasz Bem (Hungarian: Bem József, Turkish: Murat Pasha; 14 March 1794 – 10 December 1850) was a Polish engineer and general, an Ottoman pasha and a national hero of Poland and Hungary, and a figure intertwined with other European patriotic movements. Like Tadeusz Kościuszko (who fought in the American War of Independence) and Jan Henryk Dąbrowski (who fought alongside Napoleon Bonaparte in Italy and in the French Invasion of Russia), Bem fought outside Poland's borders anywhere his leadership and military skills were needed.

He was born on 14 March 1794 in Tarnów in Galicia, the area of Poland that had become part of the Habsburg monarchy through the First Partition in 1772. After the creation of the Duchy of Warsaw from the territories captured by Napoleon, he moved with his parents to Kraków, where after finishing military school (where he distinguished himself in mathematics) he joined the ducal forces as a fifteen-year-old cadet. He joined a Polish artillery regiment as a sub-lieutenant and then lieutenant in the French service, took part in the French invasion of Russia (1812), and subsequently distinguished himself in the defence of Danzig (Polish: Gdańsk) (January – November 1813), winning the Knight's Cross of the Legion d'honneur.

After the Congress of Vienna in 1815, the Duchy of Warsaw was transformed into the constitutional Kingdom of Poland, a dependent territory of the Russian Empire, and Bem became a teacher at a military college. There he carried out research on a newly designed rocket-like missile, publishing his research with extensive illustrations.

Bem became involved in a political conspiracy to restore Poland to full independence, but, when his membership in a secret patriotic organisation was discovered, he was demoted and sentenced (in 1822) to one year in prison. Although the sentence was suspended, Bem resigned his commission and moved to Galicia. There he researched steam engines and their application, and again published his results. Bem lived in Lwów (now Lviv) and Brody until 1830, and planned on writing a treatise on the subject.

When the November Uprising, an insurrection for Polish independence, broke out on 29 November 1830 against the Russian Empire, Bem immediately joined the Polish insurgents. He arrived in Warsaw, was given a major's commission and the command of the 4th Light Cavalry Battalion, which he led during the Battles of Iganie and Ostrołęka. During the Battle of Ostrołęka, Bem's forces bravely charged the Russian opponents. Although the Polish army suffered a serious defeat with a loss of 6,000 men, Bem's actions prevented the destruction of the entire army. For his valour on the battlefield, Bem was awarded the Virtuti Militari Golden Cross and promoted to the rank of Brigadier General. He was steadfastly against capitulation until the very end of the Uprising, during the desperate defence of Warsaw against Prince Paskievich (27 September 1831). Nonetheless, the Polish army was eventually compelled to lay down arms on 5 October 1831, and crossed the Russian–Prussian partitional border under the command of General Maciej Rybiński in the Great Emigration.

Bem then escaped to Paris, where he supported himself by teaching mathematics. In France, he published his next work, on the national uprising in Poland, in which he not only gave an appraisal of the 1831 insurrection, but also tried to present a programme for the continuation of the struggle for the country's freedom. During his stay in France, he collaborated with the Hôtel Lambert organization and was a member of the Historical and Literary Society.

In 1833 he went to Portugal to assist the liberal Dom Pedro against the reactionary Dom Miguel, but abandoned the idea when it was found that a Polish legion could not be formed there. While in Portugal he was the target of an assassination attempt carried out by Russian agents.

A wider field for his activity presented itself in 1848 due to the Austrian Revolution in the Habsburg Empire. First he attempted to hold Vienna against the imperial troops of Alfred I, Prince of Windisch-Grätz, and, after the capitulation, hastened to Pressburg (Hungarian: Pozsony, today Bratislava, Slovakia) to offer his services to Lajos Kossuth, first defending himself, in a long speech, from the accusations of "treachery to the Polish cause" and "aristocratic tendencies" — which the more fanatical section of the Polish émigré Radicals repeatedly brought against him. He was entrusted with the defence of Transylvania at the end of 1848, and in 1849, as General of the Székely troops, he performed miracles with his little army, notably at the bridge of Piski (now Simeria, Romania) on 9 February, where, after fighting all day, he drove back an immense force of pursuers.