Contraltos are the lowest female singers commonly heard. Unlike their male counterparts (the basses), however, roles for altos are a bit more common, especially in rock musicals. In more traditional pieces, altos are frequently middle-aged leading women, though some of those are mezzos as well. The only role demographic altos have a firm hold over is for women over sixty - which in most shows means grandmothers. In the rare case that there is a female villain in a show, she will probably be an alto.
“[…] Like a fake latina? My parents had a really really hard time when they first came here, neither of them spoke English and they were really ostracized. They didn’t want me to have to deal with the fact that some people will always look at you like you don’t belong, and I didn’t really get it, get it, until I got in this show.” - Karen Olivo about In the Heights and her latino roots.