Lucas Sinclair’s sister in Stranger Things season 3 is Erica Sinclair.
Erica is Lucas’s younger sister and the daughter of Sue and Charles Sinclair. She first appeared in season 2, but season 3 gives her a much larger role. Her sharp wit, confidence, and repeated dismissal of “nerds” quickly made her one of the show’s most memorable supporting characters.
During season 3, Dustin, Steve, and Robin recruit Erica to help investigate the secret Russian operation beneath Starcourt Mall. Her mathematical ability and fearless attitude become important to the group’s plan, and she joins the Scoops Troop in uncovering the hidden base.
The character is played by Priah Ferguson. Netflix announced Ferguson’s expanded season 3 role before the season premiered on July 4, 2019. Viewers sometimes remember Erica primarily as Lucas’s sarcastic younger sibling, but the season establishes her as an unusually capable investigator who contributes directly to the fight against the Russian conspiracy and the Upside Down threat.