The Darkness is said to be the ultimate force behind all evil in the Skylanders game series, portrayed as a large mass of onimous storm clouds. It is never effective on its own. The Darkness must channel itself through the weak, and in some cases, the idiotic.
Despite being the living embodient of evil, The Darkness itself and its sinister magic can be controlled. Spyro is the only known Skylander so far to use The Darkness and combine its power with his own to become Dark Spyro, eventually being able to control this power and using the dark magic to fight evil, but always runs the risk of being consumed by the darkness.
No one knows what The Darkness is or where it came from. Some believe that the benevolent Ancients once took their magical experiments too far and were responsible for letting the Darkness into Skylands. To repel this evil force, the Ancients developed the Core of Light, which drove out The Darkness and kept it at bay for generations.
Skylanders: Spyro's Adventure
Before the events of Spyro's Adventure, Kaos returned from his exile in the Outlands and destroyed the Core of Light, allowing him to use The Darkness to his advantage to conquer the world Skylands. After the Core of Light was fully restored by the Skylanders and the new Portal Master, The Darkness was repelled once more.
In the 3DS version, The Darkness came to the Radiant Isles and brought in Hektore, who then proceeded to capture the Mystic Seekers and forced them to create the Dark Mirror that will later shroud the Radiant Isles from the rest of Skylands. After Hektore was destroyed, The Darkness was driven away.
In Skylanders: SuperChargers, the darkness makes a return by Kaos building the Sky Eater or as he calls it, the Ultimate Doomstation of Ultimate Doomstruction. He used the last existing piece of the Darkness to build it with the first Sktylander to observe it being High Volt. In the Spell Punk Library, the Portal Master learns that the Darkness came from the Dark Rift Engine which the Ancients made but regretted it severely.
As the adventure continues, the Darkness develops a head and it learns to speak. When you reach the Sky Eater either by Flynn using his ship to drive into the Sky Eater or use a Sky Vehicle to destroy a meteorite which will allow access. Soon after, the Portal Master fights Kaos and then beats him. Kaos then "destroys" the Darkness. The song, "You Beat the Darkness" plays while credits roll in and then the Darkness re appears to fight and finish the Skylanders once and for all.
As the Portal Master and the Skylanders fight the Darkness, Rift Surge Rings begin to show and the Darkness shows his true intentions, destroy the universe, not just Skylands. Soon after, the Darkness gets eradicated from Skylands.