Sitting between mezzo sopranos and tenors, contraltos have relatively few roles in opera as little has been written specifically for them and what roles they have are usually that of maidservants, mothers, grandmothers, and friends of the heroine, but they occasionally get hardy roles, notably witches and goddesses. They also play roles originally meant for castratos (when mezzo-sopranos, countertenors, tenors, and baritones don't take them).
A number of pop singers and Broadway performers are contraltos, although they are not farther distinguished as they would be in opera. Examples include Fiona Apple, Cher, Toni Braxton, Etta James, Sarah Vaughn, Alicia Keyes, Diana Krall, Lisa Gerrard, Amy MacDonald, Yulia MacLean, Amy Winehouse, Adele, Reba MacIntire, Stevie Nicks, Katy Perry, Carly Simon, Ana Carolina, Emily Haines, Judy Garland, Chaka Khan, and Annie Lennox.
Coloratura contralto: light, agile, flexible, capable of vocal acrobatics (a rare voice).
Lyric contralto: stronger than coloratura contralto, but lighter and tamer than the dramatic contralto. Most common contralto voice.
Dramatic contralto: A powerful, rich, dark female voice and very rare.
Operatic contraltos include Ernestine Schumann-Heink, Maureen Forrester, Kathleen Ferrier, Marian Anderson, Marie-Nicole Lemieux, Nathalie Stutzmann, Ewa Podles, Anna Larsson, and Sonia Prina.
The alto range, which is below soprano, is really an easy combination of the mezzo-soprano range and the contralto range; the mezzo-soprano is the medium female voice and therefore the higher of the two.
Marian Anderson and Kathleen Ferrier were legendary operatic contraltos in their day.
Toni Braxton is a famous popular music contralto. As are Brandy, Alicia Keyes, Cher, and Blu Cantrell, among others.
Some famous contralto roles in musical theatre are Katisha (The Mikado), Dalila (Samson et Dalila) and Charity (Sweet Charity).
The alto range, which is below soprano, is really a mish-mash of the mezzo-soprano range and the contralto range; the mezzo-soprano is the higher of the two.