Hiei possibly one of the most mysterious characters in Yu Yu Hakusho, not much is really known about him such as his age or his last name. But he is 100% demon.
When he was born he was thrown off a floating island for being a boy and spent the early years of his life stealing and killing (not always to stay alive some times just for fun)
He has a Jagan eye (third eye) which he got to help him find the island he was thrown from, it also enhances his abilities. When in his full form (which is a green demon) he gets eyes all over his body.
Hiei has two weapons he is really known for, his main weapon, his katana (which he wields with deadly accuracy) and his dragon of the darkness flame (which is deadly scary), which is contained on his right arm.
He first meets Kurama and mistakes him for his enemy, then later asking him for help to steal three artifacts from spirt world (the place you go when you die). After being caught (defeated) by Yusuke, both Hiei and Kurama help him as part of their punishments.
Besides Kurama Hiei only somewhat gets along with Yusuke and that is only because he respects his strength (since he did defeated him). Him and Kuwabara on the other hand well let's just say they don't get along.
There we go every one that's the team, but I'm not done yet because there are still some things missing.