The Source of All Evil

In the Comics
"The ruler of the Underworld, The Source of All Evil is the most powerful demon in existence. The Charmed Ones first encountered the Source in the body of a demon bearing the scars of an ancient battle, but the Evil essence has possessed the bodies of numerous demons over the centuries. The Charmed Ones succeeded in vanquishing the initial demon body, but its essence was transferred into other evil entities before being banished to the Wasteland. The Source returned, briefly, years later in his earlier, scarred demon form that was ultimately vanquished."

Neena and Hogan returned to the Underworld and reported their progress to a whisp. The whisp turned out to be the essence of the Source and by the end of the issue, he had been returned in a brand new body, this time, a golem.

On the suggestion of Neena, Hogan lent the aid of his discord power and the Source used it to turn the innocents against the Charmed Ones, even Paige's husband, Henry Mitchell. With the innocents attacking, the Source chose then to reveal himself and attack.

Knowing the Source was back, the Charmed Ones vowed to end the Source once and for all.

The battle is on. The Charmed Ones collected the magic of the entire magical community in order to fight. Piper got Coop to bring her to collect Excalibur for her to use once Wyatt released it from it's stone. The combined power vanquished the Source.