Russian Empire
Though the Empire was only officially proclaimed by Tsar Peter I following the Treaty of Nystad (1721), some historians would argue that it was truly born either when Ivan III of Russia conquered Veliky Novgorod in 1478, or when Ivan the Terrible conquered the Khanate of Kazan in 1552. According to another point of view, the term "Tsardom", which was used after the coronation of Ivan IV in 1547, was already a contemporary Russian word for empire.
Russian Constitution of 1906
Prior to the enactment of the 1906 Russian constitution, the Russian Empire had been an absolute monarchy, ruled by an autocratic emperor, who was commonly referred to by his pre-imperial title of "Tsar". The precise regulations by which the Tsar exercised his imperial prerogatives were first codified in 1832, with the issuance of the "Set of Laws of the Russian Empire" ("Свод законов Российскои империи"), penned by Mikhail Speransky. These laws could be altered or repealed by the emperor. However, the autocratic Tsars were generally limited by two constraints: they and their spouses must profess the Russian Orthodox faith, and they must obey the laws of succession laid down by Emperor Paul I. Beyond that, the power of the Russian emperor was virtually limitless.