While she shares a name with the vampire couple from Wildemount, she is not a vampire and there is no evidence she bears any blood relation. Lydia appears to be human, with jet black hair and pale skin. Her features are unremarkable, and she is no great/classic beauty, though she is graceful and composed at all times. Empress Briarwood normally wears studded leather armour, with a mage’s robe over them. Her crown is a simple circlet of gold. While her clothes are simple, they are indeed quite costly.
Once a member of the Cerberus Assembly (and former student at the Soltryce Academy, though not under Trent Ikithon), she left shortly after the destruction of Vecna, citing disappointment in how the Dwendalian Empire refused to aid unless under direct threat. She arrived in Vasselheim under the name “Livia Thorne” and, as a mage, she quickly understood and respected the ‘no magic’ rules of Vasselheim, and seemed to be a model citizen.
She was an active member of the Dissenters, and in fact one of the leaders along with Ryo Yelmoira and Victor Von Vasselheim. After the destruction, she was nominated by the survivors to lead them, and by 842 was crowned Empress.
By all accounts, she has been a fair and just ruler. The only questionable moment in her young reign was when she made it legal for magics of all kinds to be used in New Vasselheim. Her reason was that it was the hiding of magic in place of religion that led to the Dissention and the One Day War. To allow all people of all backgrounds to use their talents, be they learned or granted by others, was the only way to move forward.
Nearly everyone of any rank is suspicious of the Empress. While she does well for the nation, the fact that she appears to have taken the name Briarwood is viewed with distrust
According to Victor’s surviving family, Lydia wants to destroy Vox Machina, and plans to poison them. They believe it has to do with something called The Blue Sick, which requires saltpetre.
It wasn’t until the intervention of the Agents of Numina that the truth was revealed.
Lydia was actually Lady Vex’ahlia Sylda von Musel Klossowski de Rolo III, a many times great descendant of Vex, the first to bear the name since Original Vex’s death. She was from the timeline the adventurers had accidentally created while in Draconia/Ravenia, wherein Vex’halia had gone insane trying to find Stubby.
While Vex was defeated by Keyleth (though not before she destroyed pretty much all dragons and Dragonborn in her mad vengeance), and her name sullied, there were a few of her decendants who felt she was right. One of those was Lydia’s mother, who primed her daughter to follow those footsteps.
Of course, the heir to the generations of anger, Vex III didn’t want to save her ancestor’s name… She wanted the prime-timeline STUBBY to feel their pain. A follower of Vecna, she used the Ziggurat and the Crest to power her jump through time, landing her on Wildemount in 825PD. For 10 years, she worked in secret, learning from the Soltryce Academy, finding where the items she needed were now, and planned to take over Isslyra and Vasselheim to obtain the weapons she needed.
Many of Vecna’s weapons were locked away, so under the name Livia Thorne, she aligned herself with Arkhan and Ryo and Victor to weaken the power structure of Vasselheim. Small accident, though, was that Victor found out something was wrong, and betrayed her. Her plan didn’t quite work out, leaving her underpowered and in need of saltpeter to kill the de Rollos.
Lydia was killed by the Agents of Numina and her past revealed in 845 PD. While the Agents know of her past, few others do.