Kurama,although he appears
human, is actually a youko, originally named Ryouko, who is many hundreds of years old. He had a reputation as the best thief in the Makai, but he was shot by a "hunter" and to save himself, he tore his soul from his dying body and fled to
the Ningenkai. Kurama's youko soul took over the body of the child a human woman, Minamino Shiori was carrying in her womb. When the baby
was born, she named him Shuichi.Kurama only planned to stay with his "mother" for the fifteen years it would take for his soul to heal, but over the years, she taught him what it meant to care about someone unconditionally and he couldn't bring himself to leave her. In fact, when Shiori was ill and dying of some mysterious disease, Kurama joined up with Hiei and another youkai, Gouki,
to steal the Mirror of Utter Darkness, one of the three treasures of the Reikai, and trade his life for Shiori's. He was saved when Yuusuke offered up his own life as well so that Shiori wouldn't lose her "son" and the mirror spared them, impressed by Yuusuke's noble sacrifice. Kurama joined the reikai-tantei, like Hiei, rather than going to jail, but he was glad to do it to repay Yuusuke for his life.
Minamino Shuichi's seiyuu is Ogata Megumi
By the way, just so you know, I am the official keeper of Kurama's secret about his true youko nature according to theYYH Keeper's List, so we won't tell him I just told you all.
