[BalalaikaBoy]

Norma, hands down.
Edit: Turandot comes in second imo

 

[BalalaikaBoy]

It may be difficult for anyone not a singer to answer this definitively, but I would say it would depend on the singer as much as the role. Lilli Lehmann famously said she would rather sing all three Brunnhildes than one Norma, but I suspect Joan Sutherland would have felt differently. Either part might be a candidate for most difficult female role, with Isolde very much in the running. For tenors, Tannhauser, the Siegfried Siegfried, and Tristan are all notorious killers, but I imagine Otello is a close challenger. Staying with Wagner, the Walkure Wotan requires just about everything, vocally and dramatically, a bass-baritone can give.

this is definitely true to some degree, but I think some roles are pretty universally difficult. I mentioned Norma because the singer needs to be practically switch voices depending on which part of the roles they are singing. for example
Miro o Norma: lyric soprano
Act I Trio: dramatic coloratura soprano
Casta Diva: lyric soprano/lyric coloratura soprano (depending on the key)
Ah Belo A Me Ritorna: dramatic coloratura soprano
In Mia Man: some bizarre brand of dramatic mezzo, but with Rossini-esque coloratura and a solid high C
Deh! Non Volerli Vittime: spinto soprano

while I am aware you (quite understandably) don't share my fondness for elaborate fach distincts, it's not difficult to agree that a bright, high-lying soprano voice and a dark, aggressive, witchy dramatic mezzo voice are drastically different, and that any singer able to convincingly sing the vast array of colors, weights and tessituras of Norma is nothing short of a miracle.

 

[BalalaikaBoy]

No the question of Norma and Brunnhilde, not only did Lilli Lehmann once say she would rather sing all three Brunnhildes in one night, but Callas also stated that both Isolde and Brunnhilde were a piece of cake in comparison. Admittedly she only ever sang the Walkure Brunnhilde. No doubt also she forgot that when she was singing those roles her voice had reserves of power that she could only intermittently summon up after the weight loss. Her reasons for saying so were that high notes were few and far between, that neither Isolde nor Brunnhilde asked much for the kind of vocal dexterity and flexibility of Norma, that nowhere was the voice exposed as it is in Norma and that neither of Isolde nor Brunnhilde dominated the opera in quite the same way Norma does, who is hardly off the stage once she has made her entrance.

considering that, with the exception of Marisa Galvany, Callas is the only singer who comes to mind with the vocal apparatus to sing all of Norma respectably, her comment here holds even more weight.

Nowadays, unfortunately too many ill-equipped sopranos try out the role, skating over its difficulties and ignoring its demands. I'd venture to suggest, though, that there have been far more great Isoldes and Brunnhildes than Normas since the operas were written.

most of today's "Normas" make me want to shoot myself. singers choosing the wrong rep is always a pet peeve of mine, but in this case, it's nothing short of arrogant.

When the opera was new there were Pasta and Malibran. Later Lilli Lehmann and Ponselle, and, in the modern age (ie complete performances preserved in sound) only Callas would seem to have truly embraced and conquered all aspects of this monumental role. Sutherland and Caballe were both appreciable Normas, and far and away better than anyone we will hear today, but I am not sure even they matched Callas's achievement in all aspects, that is both acting and singing.

^this. I prefer Sutherland in certain sections (she is second to none in the Act 1 trio, Casta Diva and Ah Bello), but overall, Callas wins hands down. Sutherland lacked the ability sing like a dramatic mezzo and project the aggression and mania necessary to fully capture Norma. generally, interpretation is not a huge concern of mine, but Norma is the exception. she is a scorned lover who murdered her children and wants to murder her ex-lover. to put it bluntly, Norma is a psychotic bitch, and the characterization of Sutherland, which perpetually sounded as if she were playing the Statue of Liberty, does not cut it.

 

[BalalaikaBoy]

I'd be inclined to rule out the Wagner roles. Whilst plenty of power/stamina is required, the score reveals that not much range is required by the singers. It doesn't test them nearly as much as the Wagnerians would have us believe

Most difficult? Perhaps, Lulu?

imo, the reason Wagner is difficult to sing is not the actual score, it's the way in which conductors pump up the orchestra louder than a friggin Queen concert.

 

[BalalaikaBoy]

Tristan and Norma are two obvious choices here.
As for male bel canto repertoire, I would venture to say that Assur (from Rossini's Semiramide) is very difficult and demanding, including both acting and hell of a marathon singing in the second act.

Rossini's bass roles are some of the most difficult opera roles in general.

in his day, it is likely that roles like Assur and Maometto would have been sung by low baritones/bass-baritones with darker voices rather than a real bass.

 

[BalalaikaBoy]

I think demanding can have various meanings. Not just stamina or volume or even virtuoso tricks. Why some of Mozart's female roles are very demanding as they involve bags of character and agility. For example, a great Donna Elvira is truly something special as indeed dear old Liz S was!

I think this extends to Mozart in general: whose works are, imo, an odd combination of vivid characterization but vocal lines which feel somewhat mechanical and un-intuitive on the voice.

 

[BalalaikaBoy]

Unlike Puccini, who writes big soaring lines and has the orchestra double them, Mozart leaves you on your own. He will not help you sound good if you aren't. His vocal writing requires perfect poise and technical discipline, and if you lack it everyone will hear by just how much you lack it. Singers know this; "practice your Mozart" means "mind your technique, find your weaknesses, fix them." It also means "don't force, keep it light, keep it flexible." Singers who specialize in Verdi or Wagner should practice their Mozart, even if they can't sing him well enough to perform him in public. Birgit Nilsson could never have sung the Queen of the Night successfully, but she sang her arias at parties, complete with high Fs.

I have heard this, and given her performances of Lady Macbeth's Sleepwalking Scene, I can believe it.

speaking of which, there's an exceedingly difficult role which hasn't gotten much attention on this thread