The Maelstrom is a void-like element that was created long before Ninjago existed. It harnesses the color of purple and was used by the Nindroids to fight the Ninja.
Decades before Ninjago was created, a race of aliens existed elsewhere. The aliens lived in the Void, a place full of violet and purple energy and objects, and locations. These aliens learned how to use the Void's energy to their own personal gain, and morphed the energy into a physical, humane form dubbed the Darkitect. The aliens had destroyed the rest of the Void to get more Maelstrom, and transwarped their race to the Ninjago universe.
At the time, the First Spinjitzu Master had already just created Ninjago, as he was in the midst of the war with the Overlord. The aliens knew to stay away, but they had come too far close to Ninjago. The Overlord took notice, and absorbed all of the aliens' Maelstrom in order to win the battle against the First Spinjitzu Master. He had not used the Maelstrom, however, as he created the Stone Army to turn the tide in his favor.
After the First Spinjitzu Master split Ninjago in two, the Maelstrom remained on the side that the people of Ninjago would come to live on. The aliens, who, after being left with no source of power, had fled to the stars, not even bothering to return for their Maelstrom. It remains outside of New Ninjago City, in the desert where the Anacondrai Tomb remains.
The Darkitect took refuge in New Ninjago City, dubbing himself Baron Typhonus as a dark magician. Unlike his creators, he has a new-found thirst for Maelstrom. General Cryptor discovered Maelstrom archives in the desert, and used them as a Spinjitzu element for the Nindroids.