Which actress played Sheldon's twin sister Missy?

Courtney Henggeler played Missy Cooper, Sheldon’s twin sister, on The Big Bang Theory.

Henggeler first appeared as adult Missy in the season-one episode “The Porkchop Indeterminacy,” which introduced her as a confident, socially adept contrast to Sheldon’s awkward intensity. Her character quickly attracts the attention of Leonard, Howard and Raj, much to Sheldon’s annoyance.

Missy was not a one-off character. Henggeler returned in later episodes, including the season-seven finale “The Status Quo Combustion” and the season-eleven finale “The Bow Tie Asymmetry,” when Missy attends Sheldon and Amy’s wedding. The role is sometimes confused with the younger Missy in Young Sheldon, played by Raegan Revord; Henggeler portrays the adult version in The Big Bang Theory.

Henggeler later became widely known for playing Amanda LaRusso on Cobra Kai. In the franchise’s chronology, Missy is Sheldon’s fraternal twin, not his older or younger sister, while their brother Georgie is older than both twins.