Canon: Avatar: The Last Airbender
Character: Ursa
Background: Ursa was born into a noble family in the Fire Nation. Not much is known about her childhood, but Avatar Roku was her grandfather (it is unknown whether he was her paternal or maternal grandfather.
At one point, Ursa married Prince Ozai, the second-born son of Fire Lord Azulon. The couple had two children, Princess Azula and Prince Zuko.
During the war, her nephew Lu Ten, son of Iroh, the firstborn and heir of Fire Lord Azulon, died, and Iroh failed in conquering Ba Sing Se for the Fire Nation. At that time, Ozai approached his father and asked to be made his heir, arguing that his older brother Iroh was unfit to lead the Fire Nation after his failure at Ba Sing Se. Azulon became enraged at the request, calling it dishonorable, and decided to punish him by asking Ozai to kill his own firstborn, Zuko.
Ursa learnt of this and designed a plan that she brought to her husband. While the details of the plan are not known, it resulted in the death of Azulon and the crowning of Ozai as Fire Lord. Ursa disappeared and was branded a traitor of the Fire Nation. Due to this, she was never crowned and never received the Title of Fire Lady.
That night she disappeared, Ursa woke her son Zuko up. She told him these words:
"Zuko, please, my love, listen to me. Everything I've done, I've done to protect you. Remember this Zuko. No matter how things may seem to change, never forget who you are."
Afterward, she left the Fire Nation Capital, never to be seen again.
Personality: Ursa is a noblewoman of the Fire Nation, and she married into the Royal Family. As such she is quite knowledgeable about court intrigues and politics. But most of all she is a devoted wife and mother, and she is ready to sacrifice her status, and maybe even her life, to protect her children. When her son's life was threatened by her husband's ambitions, she did not hesitate and plotted her father-in-law's death and her husband's ascent to the throne, and accepted the label of a traitor to her own country so her son's life would be spared.
While she and Zuko were extremely close and had a loving relationship, Ursa had a lot of trouble with her daughter Azula. Azula was very emotionally abusive towards her family members, and Ursa often had to discipline her. Ursa loved her daughter very much, and that aspect of Azula's personality worried her immensely. The relationship was further strained by Azula's jealousy towards her brother and her feelings of abandonment.
Abilities/Additional Notes: While Azulon, Ozai, Zuko and Azula are all fire benders, it is unknown if Ursa is also a fire bender herself. She did not have to be to marry into the Royal Family, as there are noble families with non-bender members shown in canon (like Mai).