The Ruby Ray of Ulo is a weapon used by Vilgax.
It consists of red gemstone lodged in a bracelet mounted on the back of Vilgax's right hand.
UseThe Ruby Ray of Ulo could be used as a laser projector, and was able to considerably weaken Ultimos with one shot. According to Vilgax, Ultimos' ability to survive the shot was unusual, suggesting that most other beings would be either immediately killed or left unconscious and defeated.
The Ruby Ray of Ulo returns in The Ultimate Enemy: Part 2, when he returns to his normal form. The means by which his armor and weapons return are at the moment unknown.