Arcturus

Arcturus is a mysterious character in LEGO Ninjago: Masters of Spinjitzu. Little is known about him, but he was a Serpentine General who battled Sensei Wu and Garmadon long ago. His reputation was great enough that a constellation was named after him. He is presumably deceased, likely due to his battle with the Spinjitzu Masters.

Project: Arcturus
Project: Arcturus was a rocket that was used by the Digital Overlord, another Serpentine, and the Nindroids to retrieve what remains of the Golden Weapons. It is evident that Pythor either remembered or had heard about him, and so named the rocket after him.

Codename: Arcturus
Sensei Wu remembered facing Arcturus in battle, and Garmadon noted that a constellation had been named after him, but the two were unable to guess at the meaning behind the association of his name with the Overlord's project.

Later in the episode, Project: Arcturus was revealed to be a rocket of the same name as the Serpentine. The rocket carried the Overlord, Pythor, their Nindroids, and the ninja into space, where the Overlord hoped to obtain the Golden Weapons. It is possible that the weapons ended up in the constellation Arcturus after the events of "Wrong Place, Wrong Time".

Trivia

 * Arcturus may be the Ninjago equivalent of the real-life constellation Draco, usually represented as a serpent-like dragon.
 * It is unclear which tribe Arcturus belonged to. This may hint at the existence of other tribes, or confirm the theory that Serpentine can become Generals by being the next-strongest member of their tribe when the current General perishes.
 * Arcturus was presumably defeated after the rest of the Serpentine were sealed in their tombs by the people of Ninjago; this could imply that some Serpentine escaped, or not all of them were actually sealed underground.
 * In "Child's Play", the picture of an unknown Serpentine General appears in an exhibit in the Ninjago Museum of History. It is unknown if this is Arcturus or a different Serpentine.