Ο Peter III of Russia (Peter III Fyodorovich or Karl Peter Ulrich von Schleswig-Holstein-Gottorp, 1728-1762), born Karl Peter Ulrich of Schleswig-Holstein-Holstein, was Tsar of Russia for only six months, from January to July 1762. He was born on 21 February 1728 in Germany and was the grandson of Peter I the Great. He ascended to the throne because of his kinship with the imperial family and the support he had from his aunt, Elizabeth I of Russia.

As a ruler, Peter III attempted important reforms. He introduced freedom for civility from military service and strengthened religious tolerance. Nevertheless, his behaviour, his preference for Germany and his lack of understanding of Russian traditions led to his isolation from Russian society and the courtiers.

During the period of Peter III, Freemasonry began to gain ground in the upper social classes of Russia, but it was still a young and limited movement. Catherine the Great, who succeeded him, was aware of Freemasonry, but maintained a complex and at times sceptical attitude towards it.

His wife, Catherine the Great (later known as Catherine the Great), overthrew Peter III in a coup d’état in July 1762. Peter III was imprisoned and probably assassinated shortly afterwards.