Mattie Harcourt is a doctor at the Boston General Hospital.
Mattie is an African-American woman with black hair and brown eyes.
Mattie Harcourt was in charge of the transfer of a donor heart to Perdita. Because a staged snow storm had ruled out conventional transportation, Kid Flash had to transport it by land. Mattie informed him of the medical aspects of the mission, and stressed that he had to run 3000 miles in four hours, otherwise the heart wouldn't be viable.
- In the comics, Mattie Harcourt was a friend of Supergirl (Linda Danvers). She was a medical resident in Leesburg, Virginia.
- This is Mattie's first animated appearance.