Theo Qwuynqhue is one of the Quintet, five siblings who are members of the Sinestro Corps. How and when they were selected has yet to be revealed. Theo is the second-oldest of the quintuplets and the older of the two brothers.
The Quintet first came to the attention of the Green-Lantern Corps by their horrific pattern of slaughtering the families of recently recruited Green-Lanterns, including new recruit Lantern Zevonn Parzzx. Then to instill fear in the new Lanterns they dropped the eyes of the deceased family members on top of a squad of recruits during their training exercises on a moon near Oa. Green-Lantern Saarek used his ability to communicate with the dead to retrieve an image of the attacker. The Green-Lanterns were at first confused by the identity of their attacker as it was someone they could not identify, of a species not in their database. Further communication showed the attacker(s) were all the same species.
The Lanterns then staked out the sectors and homeworlds of some of the new recruits. In Sector 1983, Ena of the Quintet was discovered by Honor Lantern Guy Gardner while she was trying to slay the family of the Green Lantern of Seekwom. She turned her ring upon herself, taking her own life rather than being taken into custody by the Green Lantern. In Sector 1852, Lantern Kilowog apprehended Theo before the Sinestro Corps soldier could kill the family of the Green Lantern of Kautnom. The remaining three siblings were located and captured before they could strike at additional Lantern family members. The surviving four members of the Quintet are currently incarcerated in the Sciencells on Oa. During the Sciencell Riots, one of the Quintet was freed by the Red Lantern Vice, only to be burned by the Red Lantern's plasma. What happened to the remaining Quintet siblings is unknown, but it is presumed that they either perished in the riots or were executed by the Alpha-Lanterns.