Paul I of Russia
Paul remained overshadowed by his mother for most of his life. His reign lasted four years, ending with his assassination by conspirators. He adopted the laws of succession to the Russian throne—rules that lasted until the end of the Romanov dynasty and of the Russian Empire. He also intervened in the French Revolutionary Wars and, toward the end of his reign, added Kartli and Kakheti in Eastern Georgia into the empire which was confirmed by his son and successor Alexander I.
Grand Duke Konstantin Pavlovich of Russia
Konstantin Pavlovich (; ) was a grand duke of Russia and the second son of Emperor Paul I and Sophie Dorothea of Württemberg. He was the heir-presumptive for most of his elder brother Alexander I's reign, but had secretly renounced his claim to the throne in 1823. For 25 days after the death of Alexander I, from 19 November (O.S.)/1 December 1825 to 14 December (O.S.)/26 December 1825 he was known as "His Imperial Majesty Konstantin I Emperor and Sovereign of Russia", although he never reigned and never acceded to the throne. His younger brother Nicholas became Tsar in 1825. The succession controversy became the pretext of the Decembrist revolt.