3. Nicole Sullivan as Jill Tracy

Appearances: 6 episodes in season 1 (episode 10, 22), 3 (episode 7), 5 (episode 20), 6 (episode 15), 8 (episode 18) | Known from: Kim Possible (2002-2007), Black-ish (2014-2019), King of Queens (2001-2007)
Jill Tracy is a patient who ends up multiple times at Sacred Heart and has the most guest appearances. She is presented from the start as an annoying patient who first lands in the hospital because she has collapsed.
She then resurfaces a few years later, and Dr. Cox and J.D. treat her. After initial indifference, they realize that she has tried to commit suicide. Lastly, she appears (as a living person) in the episode My Lunch with Cox
in season 5, one of the best episodes of the series.
After her death, Cox uses her organs for other emergency patients, but it is only later that it is discovered that she had rabies, causing other patients to die as well. This leads to Dr. Cox’s greatest breakdown.
As a recurring guest, Tracy also develops into an annoying character for the audience, but she must also be treated properly, and the small details must be paid attention to. In her brief appearance, she becomes a key figure in Dr. Cox’s story.