“ According to traditional interpretations, the sultan's letter and the Cossack response (also known as the Zaporozhian/Cossack letter to the Turkish sultan;[2] Ukrainian: Лист запорожців турецькому султанові) were written between 1672 and 1680.[2] The sultan supposedly demanded the Cossacks to surrender by boasting about his titles and power, and the Cossacks, allegedly commanded by a man named Ivan Sirko (or "Zaxarcenko"[3]) sent an insulting sarcastic reply in which they vowed to fight against the sultan.[2]”
I saw the reenactment pop up on (I think) [email protected] a few days before commenting here, thought it was a good fit due to the history you mention above.
The "Top of a bald head" belongs to Georgi Alekseyev, who was Grand Chamberlain of the court of the Russian Emperor, in charge of court finances. He was invited to pose for the role, but refused, as he felt it was undignified. Instead, Repin sketched the back of his head while Alekseyev was engaged in looking at an exhibit of prints. When he saw the painting, Alekseyev recognized his head, and was not pleased, but by then the painting was in the imperial collection.
"Artists being kinda dickish in harmless ways" is one of my favorite categories of trivia.