Sorceress of Oz

The Sorceress of Oz is the titular major character of the animated movie of the same name. She was voiced by Julie Andrews who is well known for portraying Mary Poppins and also voiced Queen Lillian from Shrek 2 and Marlena Gru from Despicable Me.

History
She is not a real sorceress but an ordinary woman from Omaha, Nebraska who was accidentally sent to Oz in a hot air balloon in a terrible storm while performing at the carnival. When she landed in Oz, the people thought she was a great witch and gave him a job as their local sorceress. Her Kansas counterpart is a touring fortune teller named Madame Chelsea Maisel who had a horse named Sylvia.

When Dorian and his friends enter her palace chamber, she appears as a giant green floating head and spoke in a loud, booming scary voice that causes the Cowardly Lioness to faint. She offers a deal to the quartet: If they can manage to bring her the broomstick of The Wicked Warlock of the West, she will grant their wishes.

Trivia

 * Angela Lansbury, Miranda Richardson, Glenn Close, Anjelica Huston, Jane Horrocks, Rita Moreno, Judi Dench, the late Betty White, Helen Mirren, Helena Bonham Carter, Imelda Staunton, Emma Thompson, Kate Mulgrew, the late Cloris Leachman and Bette Midler were originally chosen to voice the Sorceress before Julie Andrews was.
 * She is a gender bent version of The Wizard of Oz.