She is the King's Royal Sorceress and former teacher of Howl. Suliman admitted Howl was a gifted student and hoped one day he would replace her. But he never finished his training as his heart was consumed by Calcifer.
She starts recruiting wizards and witches for the King to fight the war that was taking place due to the prince of the neighboring kingdom gone missing. However, the Witch of the Waste was consumed by a demon of greed years ago and Howl's was consumed by Calcifer. She refused to turn a blind eye on either and tricks the Witch of the Waste to the castle and removes her powers.
She then tells Sophie (posing as Howl's mother) about Howl's heart and says if he takes part she would help him get his heart back, but if not, would suffer the same fate as the Witch of the Waste. Sophie then stands up to Suliman and the strength of her words temporarily removes her age curse, making Suliman realize Sophie is in love with Howl and now knows his weakness. Howl shows up in disguise as the King, but Suliman doesn't buy it and almost exposes his bird form with her magic until Sophie covers his eyes. Howl, Sophie, the Witch of the Waste, and Suliman's dog, Heen, escape the castle. Suliman gets a hold of Sophie's hat and decides to use her to find him.
Suliman forces Sophie's mother to plant a peeping bug in Howl's castle, but the Witch of the Waste grabs it and destroys it by feeding it to Calcipher, which makes him sick.
At the end of the movie, Heen is able to show Suliman that the Prince of the neighboring country is found and Howl got his heart back and found his true love. Suliman says the game is over and tries to help put an end to the war.