Nightingale

Nightingale was a female pegasus enlisted in the Royal Air Force. She is the mother of Fleethoof, and played a key role in his decision to enlist in the Royal Guard. Her death was previously covered up as a disappearance by Princess Celestia.
Not much is known about Nightingale other than she was a sergeant in the Royal Air Force when she gave birth to Fleethoof. As a foal, Fleethoof admired her, and saw her as a hero. Nightingale always encouraged Fleethoof to follow his dream, whatever it may be, even if it was to follow her footsteps and join the Royal Guard. 
Nightingale was one of the ponies selected for the Frozen North Offensive due to her meritorious service and skills in aerial combat. Although she survived the battle, she eventually succumbed to the harsh elements of the Frozen North and died of hypothermia. Her body was never recovered. 
=== Relationships ===
==== Fleethoof ====
Nightingale's relationship with Fleethoof has only ever been seen through Fleethoof's recollections, and even then it's obscure. What is known is that she loved Fleethoof very much and was always supportive of him in his ventures. Fleethoof recounted tales she had told him, and that she was the kindest mare he had ever known. She was very close to her son, and her disappearance caused tremendous grief and angst in Fleethoof that would eventually lead him into joining the Royal Guard to be like her. 
==== Night Shade ====
Nightingale knew Night Shade from the Frozen North Offensive, where the two fought together. Afterward, they attempted to help each other survive and find shelter. Nightingale shared stories of her family with Night Shade, but died in his hooves soon after, despite his best efforts to save her. It was Nightingale's death that pushed Night Shade off the brink of insanity. He carried her dog tags till his death as a memory of her and the justice he promised to get her. This would lead him to meet her son later in life.