Tsar Boris (Russian: Царь Борис) is a 1870 drama by Aleksey Konstantinovich Tolstoy, written in 1868–1869 and first published in the No.3, March 1870 issue of the Vestnik Evropy magazine.

It became the third and the final part of Tolstoy's acclaimed historical drama trilogy started by The Death of Ivan the Terrible (1864) and continued by Tsar Fyodor Ioannovich (1868).

[1] On 27 August 1868, Aleksey Tolstoy wrote in a letter to the Vestnik Evropys editor Mikhail Stasyulevich: "[As for] Tsar Boris, I'm going to start it in the nearest future: all the necessary material is at hand."

According to biographer Igor Yampolsky, Tolstoy started to recognize in him a potentially European-type monarch whose idea was to lead Russia out of its historical isolation and patriarchal stagnation into the world political arena.

While in The Death of Ivan the Terrible Maria gets horrified and frightened when learning of her husband's ambitions, in Tsar Boris she helps him with zest and cruelty, motivated by personal interests, not by those of the state.

[1] Aleksey Tolstoy, who used Nikolay Karamzin's History of the Russian State as the major source, became intrigued by and confused with the character of John, Prince of Schleswig-Holstein, princess Ksenya's fiancé and Christian IV of Denmark's brother.

[1] He applied to both Kostomarov and Baron Karl Ungern-Sternberg for help, trying to resolve a mystery of "how could Ksenya's bridegroom have fought (according to Karamzin)[2] in the Netherlands under the Spanish banner."

According to the play, when the Spanish king "rose to war, threatening to chain the free nation down," the Dutch prince "came up to help his persecuted brothers" and fight against Spain.

Then, the Impostor's plotline, initially considered to be significant, was dropped altogether, for this strand of the story would have got in the way of the play's main idea, as the author saw it.

It ends with Boris' death which is brought about not by poison but by the general anemia of a guilty man who comes to the realization of what a mistake his crime had been," Tolstoy wrote in a letter to Princess Saine-Witgenstein on 17 October 1869.

The latter's emergence Tolstoy explained in a November 30, 1869, letter to Stasyulevich: "The introduction of Mitya the Outlaw was prompted by Schiller's advice he's given through his Marquis of Posa character: "Let them treat with respect dreams of their youths."

In fact, the whole way of the Godunov character's evolution, from The Death of Ivan the Terrible to Tsar Boris, might have been the direct consequence of Tolstoy checking himself against Pushkin, according to Yampolsky.

Tolstoy's Boris was in many ways cast after that of Karamzin, who pictured the doomed ruler's tragedy in metaphysical terms, as being a price he had to pay for his bloody deed.

Acts II, III and IV should have been dated 1602 (according to the time of the Danish Prince Johan's arrival in Moscow) and 1604-1605 as for the False Dmitry-related events.

Miranda, the papal nuncio, says things that had been actually pronounced by Pope Clement VIII's legate Allessandro di Comolo who visited Moscow in the times of Fyodor Ioannovich (Karamzin, History, Vol.X, 190).