In the fictional television series ER, Lucy Knight was a medical student portrayed by actress Kellie Martin. The character was part of the show for the 5th and 6th seasons.

When she was first introduced on ER, Doug Ross called her a "by the book" medical student. Dr. Carter soon became her mentor in the ER. The two became close friends, and had even become romantically involved.

One day, a man with schizophrenia was checked into the hospital. The man managed to stab both Knight and Dr. Carter. While Dr. Corday was initally able to repair the damage to Knight's body, she soon developed complications. Dr. Corday and Dr. Romano both tried to save her life, but Knight died while on the operating table.

Dr. Carter blamed himself for Knight's death. Her death, along with the pain caused by his own stab wounds, had contributed to his abusing drugs. After Carter's return from the Atlanta inpatient clinic, his grandmother begged him to leave the ER, saying that the place killed his friend Knight, and nearly did the same to him.