Having played Jud Fry, I know that it is hard to do. To make your character 3-dimensional in the right way is very complicated, and quite often, overdone. Shuler Hensley did an AMAZING job portraying him. I will testify to the fact that Lonely Room is the hardest song to sing in the show. It's atonal and dissonant, and also very complicated to act. Also, the belt at the end is only a C-sharp, but it's harder to sing than it sounds.You have to dig into your deepest sorrow to play the character. At the same time of being a hostile, depressed drunk in a situation of unrequited love, you also have to make the audience feel sorry for you when you die.
Another very demanding role for musical theatre, although not much singing is involved, is Man in Chair from The Drowsy Chaperone. If the show is performed without an intermission, the character doesn't leave the stage but for one small song, and comes back on quickly after. You must memorize monologue after monologue, have impeccable comic timing, explore both despression and joy, and be good at connecting with the audience, because quite honestly, no one else interacts with him onstage.
For females, I'd say Elle Woods. Like Man in Chair, Elle rarely leaves the stage. When she comes on, she hardly leaves. Also, half the score is written for her and it spans almost two octaves. It's all higher belting as well.
Tracy Turnblad could be considered another one.
Updated On: 5/26/16 at 11:36 AM