Judith Klass was a female human physician in the 23rd century. She earned her M.D. at St. George's University in London, circa 2249. She met Leonard McCoy when he was an exchange student for one semester from the University of Mississippi.
She was an instructor at Starfleet Medical, where one of her students was Christine Chapel. By 2289, she was Chief Medical Officer aboard the USS Excelsior, having been a doctor for forty-three years. Doctor Klass was severely injured during the Federation/Klingon Peace Talks by the Albino. After Hikaru Sulu took command, she suggested she might retire after serving over thirty-seven years on starships. (ST novel: Excelsior: Forged in Fire) However, she did continue to serve under Captain Sulu on his first assignment as the Excelsior's Captain. (TOS - The Captain's Table novel: War Dragons)