Nephalem
From Diablo Wiki
The Nephalem are the first generation of humans on Sanctuary. They are also known as Sanctuary's Children in the Sin War books. They are the direct offspring of angels and demons, with the potential to be even greater than both. It is believed that such beings as Bul-Kathos, Rathma, and Esu, to name a few, are the first Nephalem to be born, and that their children are the current Barbarians, Necromancers, and Sorceresses whom we know today in the Diablo universe.
Due to the Worldstone, the Nephalem's power has been slowly drained with each generation, therefore making any new offspring weaker and weaker.
Speculation
With the destruction of the Worldstone, it is theorized that humanity may begin to regain their former Nephalem status in power.
