One of the reasons Handel operas went unheard for so long was the lack of voices suitable for singing the higher-voiced male roles. Not only are these pitched too high for most men, but they also require a great deal of flexibility, not formerly part of the training for most male singers. In the latter part of the twentieth century, women singers such as American mezzo-sopranos Marilyn Horne, Lorraine Hunt Lieberson and Vivica Genaux reintroduced the works to modern audiences but, while audiences were willing to hear women portraying young boys and men in traditional trouser roles such as Cherubino in Le nozze di Figaro or Octavian in Der Rosenkavalier, they were slower to accept them as the great historic and mythical heroes of Handel's operas. A solution was to transpose the roles for lower voices. For example, the great American bass-baritone, Norman Treigle, sang the title role, originally written for a male alto, in Handel's Giulio Cesare.
With the emergence of the countertenor as a generally accepted voice category, we have another choice. While Vivica Genaux sings the role of the heroic knight, Ariodante in San Diego Opera's production, the role of the villain, Polinesso (ironically originally written for a woman), is being sung by American countertenor, David Walker.
The true countertenor is a natural tenor (more rarely a baritone) with an extended range at the top. With training and practice this higher range, similar to that of a woman alto, becomes the 'natural' voice, the one in which they are the most comfortable, and the one in which they produce their best sound. They find the chest voice in the lower part of the tenor range difficult to produce satisfactorily.
At first it was thought that the high countertenor voice was suitable for chamber opera, songs and oratorios but it was too weak to project in large opera houses. Modern countertenors have disproved this. David Daniels can fill the 4,000+ seat Metropolitan Opera House with ease.
Another way for a man to sing in a high range is to use falsetto. While true countertenors, who sing in the alto range, do not do this, male sopranos must usually use some falsetto. There are a few 'natural' baritones who sing countertenor, but most of these also use some falsetto.
In the twentieth century, roles began to be written specifically for the countertenor voice, notably that of Alfred Deller (1912-1979). Modern composers who wrote for this voice include Benjamin Britten, Michael Tippett, Philip Glass and Aribert Reimann.