Midoriko (翠子) "green child" was a great Miko from the past in the anime series InuYasha. During a battle between herself and yōkai, the battle was sealed into the Jewel of Four Souls (四魂の玉, Shikon no Tama, the Shikon Jewel).
She was able to seize the souls of yōkai and purify them, this power coming from having a positive balance of the four souls within her heart, and in a time of many yōkai ravaging the earth those who possessed spiritual powers such as hers were considered to be as powerful as 100 samurai. Her spiritual power alone paled that of any other person alive, and it was said she could purify and destroy 10 yōkai at once. Her final adversary and the one that claimed her life was created by many yōkai joined and anchored within the evil heart of a human who secretly lusted for her, similar to how Onigumo loved Kikyo and created Naraku.
After 7 days and 7 nights of fighting, Midoriko realized that she would be unable to fight off the yōkai, and as she was drawn into the creature's massive jaws, she seized the spirit of the yōkai and bound it within her own with the last of her power, killing both of them and creating the Shikon Jewel, which burst from her chest, similar to how it burst from Kagome's stomach in Chapter 2 of the original Manga. Within the jewel, her soul and the souls of the yōkai she bound with it still battle on, and this is why the state of the jewel depends on who possess it.
Priestess Midoriko's name is pronounced in different ways. Most say her name as me-DOOR-ee-KO, as it was originally pronounced in the anime series; however, some say it ME-doe-REE-ko. In the anime episode 147 Sango's grandfather says it the second way.