Opul Lun Sat-Yr-Nin is a supervillainess from Marvel comics. She was a dictator who ruled her world with her lover Kaptain Briton. Opul later met Briton's counterpart, Earth-616's Captain Britain, when he was transported to Earth-839. Briton, who had been transported to Earth-616, was killed by Britain's sister, Elizabeth Braddock, when he attempted to rape her.
When Sat-Yr-9 went mad and started slaughtering her subjects, Roma sent Captain UK on a mission to capture her leading to her being overthrown and imprisoned.
Escaping through a dimension gateway that had been opened byon Earth-616, Sat-Yr-9 killed a businesswoman named Courtney Ross, and took her place. Coincidentally, Ross was Captain Britain's ex-girlfriend. As Ross, she tried to create a rift between Captain Britain and his current girlfriend Meggan Puceanu.
Sat-Yr-9 also knew about Jamie Braddock's reality warping powers before anyone else including himself did (since she knew about the reality warping powers of Jamie's alternate reality counterpart) and arranged things so that Jamie's powers would be unlocked, at the expense of driving him insane. Courtney had intended to use Jamie and his great powers as a living weapon against difficult adversaries.
Courtney used Jamie's powers to change her right-hand man, Nigel Frobisher, into a duplicate of the London crime lord, the Vixen, while changing Vixen herself into a fox. With Frobisher as Vixen, Sat-Yr-9 took over the Vixen's crime syndicate.
With her powerbase built, Courtney attacked Excalibur, revealing her true identity to them. Sat-Yr-9 tried to enslave Captain Britain, against Frobisher's advice. Frobisher rebelled and was killed by Sat-Yr-9. Excalibur managed to defeat Jamie and Sat-Yr-9 and her troops were forced to flee. Captain Britain swore to avenge Courtney's death, but was unable to track Sat-Yr-9 down.
As of late, she has joined the Hellfire Club as its White Queen, with Viper, a former HYDRA assassin, as her self-proclaimed "White Princess" and bodyguard. She has been seen publicly appearing as Courtney Ross again, trying to convince Captain Britain that she somehow is the real Courtney Ross. So far Captain Britain remains unconvinced, but hasn't moved against her.