They harvest Essence only through enemies, making them one of the more complicated classes to play. Necromancers use Essence, the very fabric of life itself. They use scythes, curved blades, and phylacteries that enhance their abilities. However, the Necromancer's mastery of the cycle of Life and Death enable them to use the very forces of darkness against themselves. And despite their heroics in the battle against the Prime Evils, Necromancers are still reviled for their usage of death magic.
The Necromancer from Diablo 2 returns in Diablo 3.