After which Russian Tsar did Georges Bizet name his opera?

Ivan IV is an opera in five acts by Georges Bizet, with a libretto by Francois-Hippolyte Leroy and Henri Trianon.

A libretto on the subject of Tsar Ivan IV "The Terrible" of Russia was offered to Charles Gounod in January 1856 by the general administrator of the Paris Opera, François Louis Crosnier. Gounod worked with enthusiasm and press announcements anticipated that rehearsals would begin that November. Although Gounod completed the work in 1857 or 1858, failure to have it performed at the Paris Opera led Gounod to use parts of the score in later works; the Soldiers’ Chorus in Faust came from Ivan the Terrible. Gounod's score was auctioned in 1963 and destroyed shortly after.

Around 1862, with Gounod's encouragement, Bizet began work on the same libretto.