The Demon Hunter was the fifth class and was announced at Blizzcon 2010 in October.
Background
The demon hunters are a group of fanatical warriors sworn to a single purpose: the destruction of the creatures of the Burning Hells.The demon hunters make their home in the Borderlands, away from the jurisdiction of any nation. At any time, over half of them are dispatched to various parts of the world to figth hellspawn. There is something in all demon hunters that gives them the strength to resist the demonic corruption that would drive lesser men to madness. They hone this power, for their resistance to this taint enables them to use the demons' power as a weapon. But their mission and their power are not all that bind them together.
The female Demon Hunter in Diablo III fled from her village as a child during a demonic invasion. She was the only survivor. After days, she was found by a Demon Hunter and was taken in as a member. Since every Demon Hunter has a story like this, it is possible that the background for the male character will be similar.