Razia Sultan (d. 1240) the only female ruler to sit on the throne of Delhi

Raziyyat-Utd-Dunya Wa Ud-Din, popularly known as Razia Sultan, was the fifth Sultan of Delhi. She was courageous, just and generous. She was the only female ruler to sit on the Delhi throne.

She was the daughter of Sultan Shamsuddin Litutmish. He had 3 sons. The eldest and heir died prematurely The other two were more interested in the indulgence of royal pleasures rather than leadership. Razia administered Delhi (1231-2) when her father was busy in the Gwalior campaign. Litutmish nominated her to succeed him.
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On his death Ruknuddin Firuz , her half brother, succeeded him and his mother, Shah Turkan, wanted Razia executed. But Razia instigated the general public against him. Ruknuddin and his mother were assassinated.

Razia, a female, was now Sultan.She adopted masculine attire in court and on the battlefield.She believed in her supremacy as a ruler and took the title Sultan - (she refused to be called Sultana because it denoted a wife or mistress of the Sultan).

Her reign was short. She was a great leader who cared deeply about the empire and was popular with her subjects. She expanded the territory of the state, and fostered peace and prosperity.
There was unfortunately resentment against her and she reigned for less than years (1236-40) .

She married one of the rebel leaders - Ikhtiyaruddin Altunia in an attempt to regain the throne but was defeated by her half brother and successor Muizuddin Bahramin in October 1240 . She was killed shortly afterwards.

Sources
Wikipedia
RISE: Extraordinary Women of Colour Who Changed the World by Maliha Abidi