Rubeus is one of the commanders of the Negamoon Family who works for Prince Diamond. He travels around in a UFO and has the Negamoon Sisters working for him. His name is derived from the gemstone Ruby.
Rubeus was the first to come into the past to look for Rini and the silver crystal, sending the Negamoon Sisters to capture Rini and take over crystal points in Tokyo. Wiseman was advising him. All six of them first appeared in Episode 14.
Each of their plans were foiled, and eventually there was a showdown between the Sailor Scouts and the Negamoon Sisters, with Rubeus fighting Sailor Moon. Sailor Moon defeated him with Moon Scepter Elimination, and he retreated with the Negamoon Sisters.
After the Negamoon Sisters turned good, Emerald, who did not get along with Rubeus, came to tell him that Diamond was going to kick him out because of his failure. He captured the other Sailor Scouts, telling Sailor Moon to bring Rini to him.
Sailor Moon arrived to face him, but Rini followed her there, and both were teleported into the ship. The ship entered space, and Rubeus fought Sailor Moon. They entered several beam struggles, with Rubeus overpowering Sailor Moon, and at one point, he turned the gravity on to maximum capacity, but Sailor Moon was still able to stand. Meanwhile, Rini discovered a crystal in the middle of the room that was Rubeus's source of power. As Rubeus attempted to stop her breaking it, Sailor Moon attacked him, forcing him to fight her while Rini broke his power amplifier, releasing the other Sailor Scouts and causing Rubeus to lose all his power, and Sailor Moon defeated him.
Rubeus programmed his ship to selfdestruct in an attempt to kill the Sailor Scouts, but they teleported off with Rini. Emerald appeared, and Rubeus asked her to take him back to the future, but instead she told him that he "struck out" and left. The ship exploded, killing Rubeus.
Rubeus can throw several small energy balls at once. He can also shoot bolts of dark energy, and his strongest attack is a dark energy beam.
He can also teleport, but loses all power when Rini destroys his power source.
- The way Rubeus dies is similar to Evil General Durahan from Monster Rancher; both are on a ship programmed to selfdestruct after losing a beam struggle to a protagonist, and the good guys teleport off. They both also have a confrontation with a female villain (Emerald leaving Rubeus for dead, and Durahan killing Lilim for her betrayal) before the ship explodes, though Durahan's ship is not destroyed by the selfdestruct, but rather shot down by Moo's troops.
- Rubeus is a lot like Jedite from A Moon Star is Born to Fight to the Finish only stronger and in some ways more competent.
- Rubeus and Emerald's rivalry is just like Neflite's and Zoycite's except Neflite betrays his allies through a change of heart while Rubeus betrayed the Negamoon Sisters out of greed!
- Rubeus initially seems like the Sailor Moon R counterpart of Queen Beryl, with Wiseman as the Negaforce (a role Wiseman keeps in the end), until Emerald appears, revealing she and Rubeus are both commanders for Prince Diamond.
- Rubeus is one of three major villains to not find redemption in Sailor Moon R, other two being Emerald and Wiseman.
Voiced by Robert Tinkler