Maria Stuarda and Roberto Devereux, which both feature Elizabeth I in a leading, though not title, role.
The first opera is based on Schiller's play, Maria Stuart, and like the Vanessa Redgrave/Glenda Jackson movie, commits the wild inaccuracy of having Mary, Queen of Scots and Elizabeth I meet. Donizetti's librettist Giuseppe Bardari creates a love/hate quadrangle: Elizabeth loves Leicester; Leicester loves Maria; Maria hates Elizabeth; Elizabeth hates Maria. From that you get three acts of bel canto drama, confrontation, but no mad scene. In the end:
Maria's friends lament her fate, and she, facing death calmly, tries to comfort them and give them strength. As the cannon sounds the signal for her execution, Cecil asks for her last requests. She forgives Elisabetta and prays for a blessing on her and the kingdom. She tries to calm the grief-stricken Leicester and hopes that her innocent blood will placate the wrath of Heaven. She goes resolutely to her death as her friends grieve over her fate.
Roberto Devereux gives us the triangle of Elizabeth and Essex and Sara, the Duchess of Nottingham, whose husband plots the death of Essex. There's a great love duet between Essex and Sara--and a tremendous mad scene for Elizabeth before Essex's offstage execution. She abdicates at the end.
There is really a fourth opera in Donizetti's Tudor series, Il castelo di Kenilworth, but even though it features the really great triangle of Elizabeth, Leicester and his wife Amy (Amelia), it does not get as much attention because it is not a tragedy. Amy survives attempted poisoning and does not fall downstairs. The opera is a comedy (not a funny comedy but a comedy in the classic sense): Elizabeth gives her blessing to Amy and Leicester and everybody is happy--except for the villain, of course.
Donizetti wrote other operas with an English or Scottish setting: Lucia di Lammermoor most famously, but also Rosmunda d'Inghilterra about the Fair Rosamund, Henry II and Eleanor of Aquitaine, and Emilia di Liverpool. English royalty also appear in L'assedio di Calais, with Queen Isabella begging King Edward III to show mercy to the burghers of Calais.
Donizetti was extraordinarily prolific, considering that he died when he was 56 years old, composing nearly 75 operas, 16 symphonies, 19 string quartets, 193 songs, 45 duets, 3 oratorios, 28 cantatas, instrumental concertos, sonatas, and other chamber pieces.
To conclude this operatic post--Rossini also wrote an opera featuring Elizabeth I and Leicester: Elisabetta, regina d'Inghiliterra, which included snippets of music from earlier work--and then Rossini used music from it in later work. Leicester is secretly married to Matilde who is Mary, Queen of Scots' daughter (in this ten-minute survey of the opera, you know she's from Scotland because she's wearing a kilt/plaid!) Elizabeth sends Leicester to prison along with his wife and her brother, Enrico. The Duke of Norfolk is the villain and tries to kill the queen! She frees Leicester, Matilde and Enrico at the end after they save her life.
All four of these operas offer interesting interpretations of history! As this review of a 2010 production of Maria Stuarda comments:
There's a fond belief that Donizetti's Maria Stuarda is about Tudor history. It is, to the extent that its chief characters are Mary, Queen of Scots and Elizabeth I, and others have recognisable names such as Robert Dudley, the Earl of Leicester and Sir William Cecil. . . .Yet Donizetti himself was none too interested in facts. You can no more rely on his 1834 bel canto opera to untangle the English Reformation crisis for you than expect Hamlet to throw light on the Danish succession.
That's opera, doc!