Peter III (February 21, 1728 - July 17, 1762) (Russian Пётр III Федорович (Pyotr III Fyodorovitch)) was Emperor of Russia for six months in 1762. He was mentally weak and very pro-Prussian, which made him an unpopular leader. He was assassinated as a result of a conspiracy allegedly led by his wife, who succeeded him to the throne as Catherine II.

Peter was born in Kiel. His parents were Karl Friedrich, Duke of Holstein-Gottorp (nephew of Charles XII of Sweden), and Grand Duchess Anna Petrovna, a daughter of Emperor Peter the Great of Russia and his second wife, Catherine I of Russia (a former Latvian peasant, Martha Skavronskaya). In 1739, Peter's father died, and he became Duke of Holstein-Gottorp as Karl Peter Ulrich. Two years later, Karl Peter Ulrich's aunt Elizabeth, became Empress of Russia, and brought Peter from Germany to Russia and proclaimed him her heir. She arranged for Peter to marry Princess Sophia Augusta Frederica of Anhalt-Zerbst, who formally converted to Russian Orthodoxy and took the name Ekaterina Feodorovna, or Catherine. The marriage was not a happy one, and Catherine took numerous lovers, as did her husband.

Peter favored Prussia in many respects: after he gained the throne in 1762, he withdrew from the Seven Years' War and made peace with Prussia, in which Russia did not gain anything,in spite of Russia's virtual victory in the war. He formed an alliance with Prussia and planned an unpopular war against Denmark in order to restore Schleswig to his Duchy of Holstein-Gottorp. He also attempted to force the Russian Orthodox Church to adopt Lutheran practices.

Catherine, along with her lover Grigori Orlov, planned to overthrow Peter. He was arrested and forced to sign his own abdication; Catherine became Empress with wide popular support. Shortly thereafter, Peter was killed while in custody. While Catherine did not punish the responsible guards, doubts remain as to whether she ordered the murder.

In December 1796, Peter's son the tyrannical Emperor Paul, who disliked his mother, arranged for his remains to be exhumed and then reburied with full honors in the Cathedral of the St. Peter and St. Paul fortress, St. Petersburg.

|- style="text-align: center;" | width="30%" |Preceded by:
Elisabeth | width="40%" style="text-align: center;" |Emperor of Russia
January 5 - June 28, 1762 | width="30%" |Succeeded by:
Catherine II