(This article is heavily indebted to the chapter Don Carlo in Volume III of Julian Budden's authoratative The Operas of Verdi.)
The historical Don Carlos, Prince of Asturias.Don Carlos, Don Carlo, or whatever you call it is Verdi's darkest opera, a masterpiece that suffered a difficult premiere, heavy cuts, and complex linguistic issues to eventually emerge as one of the composer's most popular operas. But that process took ninety years, from the work's premiere in 1866 to a hugely successful Covent Garden staging in 1956 that gave Don Carlos its much deserved place in the international repertory.
The opera was originally written for the Paris Opera, and was the third "grand" opera that Verdi wrote for that theater. Verdi used a French libretto based on Don Karlos, a German play by Friedrich Schiller. Schiller's drama was based on the life of the son of King Philip II, the "Catholic King" who held Spain in an iron grip. Schiller's hero was a romanticized version of the real infante of Spain, a dangerous, violent prince entirely unsuited to the difficult business of ruling. The real Carlos was locked up by his father, and died in isolation.
On the night before the premiere in 1867, Verdi found out that the five-act opera would run past midnight, making it impossible for Parisians living in the suburbs to catch trains home. The composer was forced to cut the first ten minutes (the scene with the woodcutters) to compensate.
Unfortunately, he left in the scene between King Philip and the Grand Inquisitor. At the moment when the exasperated King bursts out with "Tais-toi, prétre!" ("Shut up, priest!") the very Catholic Empress of France turned her back on the stage. This ensured that Don Carlos bombed in its opening run, joining La Traviata, I Vespri Siciliani and Stiffelio in the ranks of Verdi works that stiffed on opening night.
As the opera moved beyond its Paris run, Verdi made more cuts. First to go was the "La Peregrine" ballet, a requirement for Paris performance that added nothing to the opera's plot, and the insurrection scene that ends Act IV. But even with trims, the new opera failed to catch on.
In 1883, Verdi worked for nine months to prepare a four-act version (now called "Don Carlo"), to a new Italian translation based on the French libretto. Not content with removing the woodcutters, he axed the first act. As a result, Carlo's romanza "Je le vieux" became "Io lo vidi," and was moved from the forests of France to the austere Spanish monastery of San Yuste.
The composer made extensive revisions to his new first act, rewriting the crucial duet between Posa and the King to bring the work closer to Schiller's play and adding some of the excised Act I material to give the work some context. He slashed the scene before the ballet, and revised the prison scene between Carlo and Posa. Finally he changed the ending slightly, cutting out a chorus of Inquisitors and giving the final scene a typical fortissimo ending.
This four-act Carlo proved popular with audiences. But he wasn't done yet. In 1886, Ricordi, Verdi's publishers put out a five-act version of the score, giving opera houses the option of restoring the Fontainebleau scene as a curtain raiser with "Io lo vidi" back in its proper place.
This led to further revisions, a new shortened version of the chorus before "Io lo vidi" and some more tweaks to the later acts. In 1956, an historic production at Covent Garden made this opera popular in its five-act version, and the advent of the recording industry has ensured that multiple revised (and unrevised) versions of the opera have been recorded.
Finally, some conductors (most notably James Levine) have brought back the long-silent woodcutters, claiming that the opening scene in the forest makes more dramatic sense than the abrupt horn-calls that start the opera. The Levine recording with the Metropolitan Opera forces is the only one in the catalogue that includes this scene in its proper place at the start of the opera.
Today, all three versions of Don Carlo/s are performed. The French conductor Bertrand de Billy has performed the original, five-act 1867 version of the opera in Vienna and Barcelona. The Met and Covent Garden favor the 1886, with the first act restored. But there is also an argument to be made for the concise power of the four-act 1883 version, which packs the drama into a tighter structure. It makes the whole opera darker and more oppressive, but in Don Carlos, or Don Carlo,, that's not a bad thing.