Alexei Arakcheev (1769-1834) was a Russian general and politician who served as one of Alexander I's most trusted advisors. The period when he was at the height of his power was known as the Arakcheevschina ('Arakcheev regime') which has become byword for a harsh, repressive military regime. His influence helped Tsar Alexander I transform himself from the liberal, reformist man of his youth to the more reactionary autocrat of his later years. Arakcheev was also responsible for implementing Alexander's ill-advised policy of military settlements, where unfortunate serfs would be locked into military and agricultural service.
Dmitry Golitsyn (1771-1844) was a Russian general, military strategist and governor of Moscow who wrote several books on warfare. His wife Natalie Tchernyshova was portrayed as the Queen of Spades in Pushkin's famous story of the same name (read online here).
Alexander Shishkov (1754-1841) was also a statesman who served under Alexander I. He was a fervent Slavophile, meaning that he believed in the expansion of the Russian Empire to include all Slavic peoples, and in the supremacy of Russian culture and values over Western European ideals such as democracy and liberalism.
Photius of Constantinople (c. 810-893) was an influential Patriarch of Constantinople who had an enormous impact on the development of the Orthodox Church. He was a key figure in the conversion of the Russians to this church.