In the Hindu epic, the Mahabharata, Amba was the oldest of the daughters of the King of Kasi. She and her sisters Ambika and Ambalika were abducted from their swayamvara by Bhishma.

Amba had already chosen the husband she wanted -- King Salva. Bhismha released her, and she went to Salva. But Salva rejected her since she had been carried off by an abductor.

Amba then went to Bhishma, but he could not marry her because of his vow of celibacy. He had actually stolen her to be the wife of the young King Vicitravirya -- but the King would not marry her, because she was in love with Salva.

Completely disgraced, Amba swore vengeance on Bhishma, no longer desiring marriage, home, or happiness. She dedicated herself to asceticism, and was granted a boon by Shiva.

Amba immolated herself and was reborn as the daughter of King Drupada. She practiced the arts of war as she was growing up. Her father sent her into exile, where by prayer she was transformed into a man, Sikhandin.

When Arjuna fought Bhishma, late in the Battle of Kurukshetra, Sikhandin was Arjuna's charioteer. Note that as Drupada's offspring, she is Arjuna's sibling-in-law, since he is married to Draupadi. As Sikhandin, Amba fought Bhishma, and shielded Arjuna from him. Bhishma would not fight her because she was born a woman.