It seems that many eons ago, beyond counting, there was a Buddha named Many Jewels. At one gathering of his monks and lay followers, he was approached by a princess of the land, Yeshe Dawa—Wisdom Moon—who in his presence first aroused bodhicitta, the intention to seek enlightenment for the welfare and liberation of all sentient beings, and took the vow before him to enact this aspiration.
Afterward, some of the monks approached Yeshe Dawa. They praised her intention, but offered their opinion that she would be much better suited to benefit beings in a male form, and that she should also pray to be reborn as a man. Yeshe Dawa was taken aback by this; such ideas did not agree with her understanding of the Buddha’s teaching that all beings equally have the potential to attain enlightenment.
Yeshe Dawa was confident in her understanding and of strong character, so she formed the opposite aspiration: she vowed to be reborn only in female form in order to effect beings’ liberation that way and counteract such low notions. And so she did, sincerely and diligently practicing the path to enlightenment in female incarnation after female incarnation. One of these lifetimes was in the presence of another Buddha named Ratnasambhava. It was he who declared that her name should be Tara, “She Who Liberates,” and that’s how she has come to be known in her enlightened appearance.
The story of Green Tara is from www.ewambuddhagarden.org/tag/21-taras