Green dragon

The Unidentified Dragon was a female Dragon that lived during the period of time before The War. She ended up having one known egg.

History
Her history is unknown, but at some point during her early life, the Unidentified Dragon found a mate, had an egg, and made a nest in a high mountain located in the Fire Nation. The location of her nest was mapped out by a mapmaker and sold at a cheap price. One of these maps fell into the hands of poachers, while another fell into the hands of Kuzon and his friend, Aang.

Some time after this, her egg was threatened when the poachers distracted her. One of the poachers lured her out of her cave, allowing the others to grab her unborn child. Luckily, however, Avatar Aang and Kuzon stumbled upon the poachers, and, using Kuzon's Firebending abilities, tricked the poachers into thinking she had returned. They ran off, but her egg was nearly smashed, when she returned and knocked it out of Aang's hands, thinking they wanted to steal her egg.

Luckily, Aang caught it just in time and it was revealed that they were no threat to her or her child. She was grateful, but would not take them for a ride as Kuzon wished.

Her life after this point is not known, but she and her child presumably perished during Sozin's Dragon Purging. This story was later told by Aang to Zuko.

Trivia

 * There are six known Dragons with her introduction; Sozin's Dragon, Fang, Ran and Shaw, herself, and her child (though it is not yet born during "Dragon Days").