What is the first name of Sheldon's twin sister?

Sheldon Cooper’s twin sister is named Missy. Her full name is Melissa “Missy” Cooper, and she is Sheldon’s fraternal twin rather than his identical twin.

Missy appears in The Big Bang Theory as a confident, socially skilled contrast to Sheldon’s academic brilliance and awkwardness. Sheldon often treats intelligence as the defining measure of a person, while Missy is more perceptive about relationships and everyday situations. Her arrival in Pasadena immediately catches the attention of Leonard, Howard, and Raj.

The family background is expanded in Young Sheldon. Missy and Sheldon were born on February 26, 1980, in Galveston, Texas, and grew up in the fictional town of Medford with their older brother, George Jr. Their mother is Mary Cooper, while their grandmother, Connie Tucker, is the beloved “Meemaw.”

A common mix-up is confusing Missy with Mary, who is Sheldon’s mother, or Meemaw, who is his grandmother. Mandy is an unrelated character in the wider franchise, introduced as Georgie Cooper’s partner.