Dr. Luka Kovač is a fictional character portrayed by Croatian-born actor Goran Višnjić. Visnjic's character was added to the cast at the beginning of Season 6 (1999) following the mid-season 5 departure of leading character Doug Ross, played by George Clooney. Luka later moved to the United States of America some time after that for a fresh start and later began working as a physician at County General ER but evidence he suffered from both survivor's guilt and PTSD soon emerged, largely in terms of his personal relationships.