!!Dr. Donald Westphall (Ed Flanders)
Chief of Medicine of St. Eligius, widower and father of Elizabeth and Tommy.

* BenevolentBoss
* TheChainsOfCommanding: Seems to bear the weight of both his staff and patients, especially when his community outreach programs have disastrous consequenses
* DarkAndTroubledPast: Survived an apartment fire that killed most of his family when he was six years old.
* EmptyNest
* AFatherToHisMen
* TheFettered
* {{Mentor}}: To Dr. Jack Morrison in particular.
* ReasonableAuthorityFigure
* RaisedCatholic
* {{Southies}}: Westphall grew up in South Boston.
* TakeThisJobAndShoveIt: Following its takeover by an HMO, Westphal resigns from St. Eligius by dropping trou and telling new boss John Gideon "You can kiss my ass, pal".
* TranquilFury: After Peter White is [[spoiler: found not guilty for rape]], Westphall makes him aware that he not only is disappointed in him, but now has has no respect and utter contempt for him as a human being.
* VerbalTic: Has a tendency to address people as "pal" or "lady".

!!Dr. Ben Samuels (David Birney)
* ChuckCunninghamSyndrome: While billed second only to Ed Flanders, his character becomes less prominent over the course of the first season. He is neither seen nor heard from again after the 20th episode of the season, and no explanation is given.
* ReallyGetsAround: A subplot of the pilot episode involves Samuels telling all his sexual conquests that he's contracted a venereal disease.

!!Dr. Daniel Auschlander (Norman Lloyd)
The hospital's avuncular Chief of Services, a liver specialist who has been diagnosed with [[{{Irony}} liver cancer]].

* BadassGrandpa: His grandchildren are seen from time to time.
* CoolOldGuy: More affable and mischievous than Westphall or Craig.
* DeadpanSnarker
* {{Mentor}}: To Luther Hawkins.

!!Dr. Mark Craig (William Daniels)
Ill-tempered Chief of Surgery at St. Eligius.

* BadassMustache
* BreakTheHaughty
* CatchPhrase: "Oh, for crying out loud!"
* TheDeterminator
* DrJerk: Especially earlier in the series. In the second episode, after saving a man's life with a bypass operation, he comments to the patient's young, chubby son that his son's a doctor, and that maybe the younger Craig will operate on him someday.
* GoodIsNotNice: Type 2/Type 4. He is very blunt to the point of rudeness. He is impatient, fussy, and arrogant. What drives him, though, is a deep conviction in the preciousness of life, and he will not tolerate any less of others than he does himself.
* {{Mentor}}: A reluctant one to Dr. Erhlich.
* TheNapoleon

!!Dr. Hugh Beale (G. W. Bailey)

* ChuckCunninghamSyndrome
* DeepSouth
* TheShrink

!!Dr. Victor Ehrlich [[spoiler: born Bernard Oseransky]] (Ed Begley Jr.)
Tall, blonde, bespectacled surgical resident from California, and usually on the receiving end of Dr. Craig's wrath.

* BelligerentSexualTension: Throughout season 5 with Lucy Papandrao.
* CharacterDevelopment: Matures both as a doctor and as a person to the point where he is HappilyMarried with Nurse Lucy Papandrao.
* DrJerk: A much milder case than Dr. Craig, though.
* HawaiianShirtedTourist: He usually wears Hawaiian shirts with neckties as part of his hospital attire.
* HugeGuyTinyGirl: A non-sexual example: he is at least a foot taller than his fellow surgical intern Jackie Wade.
* InnocentlyInsensitive: When Dr. Martin returns to work [[spoiler: after her stay in the psych ward following her second rape]], he manages to be even more insulting while apologizing for his past behavior.
* NoSocialSkills
* PhraseCatcher: Particularly through season 2, where every major character utters a variant of "You're a pig, Ehrlich."
* SurferDude: Before coming to Boston, Ehrlich was one of these in California. His friend Dogger still is.

!!Dr. Peter White (Terence Knox)
A resident with trouble juggling his work and family responsibilities. He begins a long mental and emotional slide in season 1 that only gets worse as the show goes on.

* DrugsAreBad
* FaceHeelTurn: Irredeemably so after [[spoiler: he begins raping women at the hospital, including fellow resident Cathy Martin]].
* KilledOffForReal
* LaserGuidedKarma: [[spoiler: When Shirley Daniels guns him down in the morgue following his rape of several women, including Cathy Martin, her first shot is right in the crotch. "Goodbye, Peter."]]
* SanitySlippage

!!Dr. Wayne Fiscus (Howie Mandel)
A sarcastic emergency medicine resident.

* AmazinglyEmbarrassingParents: His mother's arrival interrupts one of his sexual trysts, and she tells his co-workers a particularly mortifying story about his childhood.
* BigApplesauce
* JewishMother: Frieda Fiscus
* LikeBrotherAndSister: With Dr. Wade.
* LookingForLoveInAllTheWrongPlaces
* ManlyTears: When he, Shirley Daniels and Jackie Wade can't revive Wendy Armstrong after her suicide attempt.
** Also happens right after he wakes up for the first time after being shot. When he sees his surgical scar on his chest, he weeps.
* TheStoner: From time to time, he mentions his drug experimentation while at Tulane.

!!Dr. Jack Morrison (David Morse)
Compassionate resident who often has trouble with trusting his own judgement and remaining objective about his patients.

* ButtMonkey
* DesignatedVictim: Starting in season 2, something bad would usually happen to Morrison.
** Season 2: His wife Nina dies after slipping and hitting her head in the bathroom. He is cut from the residency program. Is only reinstated because a slot opened up after Wendy Armstrong's suicide.
** Season 3: Faces the end of his career over a WorthlessForeignDegree
** Season 4: Injures himself while running to make rounds and slipping on vomit. Son Pete is kidnapped. Raped while doing a Westphall-mandated community outreach service in a local prison.
** Season 5: Suffers from PTSD as a result of his rape. His attacker escapes from prison and stalks his family. Son Pete inadvertently shoots his attacker dead.
** Season 6: Second wife Joanne moves back to Seattle after her first husband sues for custody following the death of Morrison's attacker.
* TheLostLenore: Nina. Much of Morrison's arc in season 2 is him dealing with her sudden death.
* TraumaCongaLine: And how.
* WorthlessForeignDegree: In the pilot episode, Morrison tells a patient that he had to go to medical school in Mexico because his grades were not good enough for American universities. In season 3, it is revealed that the school was a shady "accelerated" program that counted experience instead of giving a full medical training, and Morrison has to fight to keep his job.

!!Nurse Helen Rosenthal (Christina Pickles)

* DrugsAreBad
* SerialSpouse: Already on husband number four at the beginning of the series. Her affair with Richard Clarendon doesn't end in marriage, but develops into a long-term cohabitation.
* YourCheatingHeart: Her fourth husband leaves her in season 3 because of her affair with Richard Clarendon, the union negotiator. Apparently, this happens so often that four of her five children aren't particularly fazed by it.

!!Dr. Vijay Kochar (Kavi Raz)
* ButtMonkey: Frequently the target of Dr. Craig's racism.
* DemotedToExtra: Was a regular during season 1 and 2, only billed as a guest star thereafter.

!!Dr. Annie Cavanero (Cynthia Sikes)
An OB-GYN who is just past her residency.

* ChuckCunninghamSyndrome
* MarriedToTheJob

!!Dr. Philip Chandler (DenzelWashington)
* BillingDisplacement: Appears front and center on the DVD box despite him being just one part of an EnsembleCast, arguably a more minor character than fellow residents Jack Morrison, Victor Erhlich or Wayne Fiscus.
* LonelyRichKid
* TookALevelInJerkass: When he comes back from corporate training with St. Elgius' new parent company, he really rubs the other residents the wrong way.
* WellDoneSonGuy: Chandler's main motivation for getting into medicine was to please his father.
* WrittenInAbsence: Was off in Missouri for training when DenzelWashington was filming a movie.

!!Nurse Shirley Daniels (Ellen Bry)
A younger nurse who usually associates with the residents.

* AxCrazy: After being released on bail before her trial, Shirley exhibits no remorse for [[spoiler: murdering Peter White in cold blood]]. On her first shift back in the ER, she pulls a gun out on a patient and refers to him as "Peter".
* HypercompetentSidekick
* TheBusCameBack

!!Dr. Wendy Armstrong (Kim Miyori)
* BigEater: Revealed to be [[spoiler:bulimic]].
* DrivenToSuicide
* KilledOffForReal

!!Dr. Cathy Martin (Barbara Whinnery)
Pathology resident with a spacey demeanor, heightened sexuality, and a tendency to dress in black.

* BrokenBird: Especially after [[spoiler:being raped. Twice]].
* BunnyEarsLawyer: It is revealed in "Rough Cut" that she had the highest score out of the first-year residents' board certification exams. A brief scene with her after she switches to psychology indicates she's particularly skilled with younger patients.
* CharacterizationMarchesOn: After [[spoiler:being raped]], Martin is not quite as spacey; she switchers her residency to psychology and stops dressing in black.
* CloudCuckoolander: At one point, after Ehrlich comments "Is there an echo in here", she says "I don't know. Is there? Hello?"
* CreepyMortician: A mild case.
* TheReasonYouSuckSpeech: Gives a few to Peter White [[spoiler:after he rapes her]].

!!Dr. Jacqueline Wade (Sagan Lewis)
Mature and capable surgical resident from Lewiston, ME; a friendly rival to Dr. Erhlich.

* AscendedExtra: Has one line in the pilot during a grand rounds scene, then becomes a RecurringCharacter later in the season. She gets her PromotionToOpeningTitles in season 6.
* DeadpanSnarker
* HugeGuyTinyGirl: Fellow residents Victor Ehrlich and Jack Morrison tower at least a foot over her.
* LikeBrotherAndSister: With Dr. Fiscus.
* MarriedToTheJob: Wade's eleven-year marriage ends in season five, as the long hours of her residency leave husband Robert to seek affection from a younger woman.
* OnlyChildSyndrome
* PluckyGirl
* ShorterMeansSmarter

!!Nurse Lucy Papandrao (Jennifer Savidge)
* AscendedExtra: Goes from an uncredited BitCharacter in the pilot to a more prominent RecurringCharacter in season 3, then a PromotionToOpeningTitles in season 6.
* DefrostingIceQueen: A drunken liason with Victor Ehrlich in season 5 results in a serious relationship, and the characters are HappilyMarried by the end of the series.
* TheSnarkKnight

!!Luther Hawkins (Eric Laneuville)
* OrderliesAreCreeps: Averted. Luther is the one person any doctor, nurse or patient would be glad to have around.
* UncleTomfoolery: Chandler calls Luther out on this in "Equinox".

!!Joan Halloran (Nancy Stafford)
* DefrostingIceQueen
* HeelFaceTurn: Introduced as someone who would butt head with the doctors over the hospital's expenses.
* PutOnABus: When Ms. Stafford left to play Michelle Thomas on ''Series/{{Matlock}}''.

!!Dr. Robert Caldwell (Mark Harmon)
* BusCrash: Mark Harmon left the show halfway through season 4 when his character contracted AIDS. In the series finale, the characters receive word that Dr. Caldwell has died.
* ByronicHero: Particularly during season 4, when his impulsive and reckless side comes to the surface.
* DatingCatwoman: In season 2, he's involved romantically with Joan Halloran, who begins as an antagonistic character that clashes with the doctors over the hospital's expenses.
* PornStache: In the first half of season 2, Mark Harmon had a very thick mustache. He gets rid of it in the episode "A Pig Too Far", but not before walking around with it half-shaved off.
* TookALevelInJerkass: In season 4 before he contracts AIDS.

!!Dr. Eliot Axelrod (Stephen Furst)
Nervous medical student introduced in season 2. He becomes a resident in the next season.

* {{Adorkable}}
* BigEater: One small arc in season 4 has Eliot and his girlfriend go on a diet. She does better than he does.
* KilledOffForReal
* MoralityPet: He becomes this for Mrs. Hufnagle.

!!Dr. Michael Ridley (Paul Sand)
* TheShrink
* SuspiciouslySimilarSubstitute: Averted somewhat; while Ridley is a replacement for Dr. Beale, their demeanors are pretty different.

!!Dr. Simon Weiss (Philip Sterling)
* TheShrink: The longest lasting psychiatrist character, although less prominent than Beale or Ridley.

!!Warren Coolidge (Byron Stewart)
* GentleGiant: At 6' 8", he towers over patients and doctors. Used to moving effect in "Weigh In, Weigh Out", where he fulfills a dying man's request to be rocked like a baby.

!!Dr. Roxanne Turner (Creator/AlfreWoodard)
* DeepSouth

!!Dr. Carol Novino (Cindy Pickett)

!!Dr. Seth Griffin (Bruce Greenwood)
* HeelFaithTurn: After possibly contracting AIDS, Griffin becomes a born-again Christian when he meets the new hospital chaplain.
* SmugSnake: Griffin at least started out this way, particularly when he tried to pit fellow first year residents Carol Novino and Susan Birch against each other. Birch ends up taking the fall for a patient death for which Griffin was responsible and is kicked out of the residency program.

!!Dr. Paulette Kiem (France Nuyen)
* ReasonableAuthorityFigure

!!Dr. John Gideon (Ronny Cox)
* BadBoss
* ObstructiveBureaucrat

[[folder:Patients and their families]]
!!Stephen McAllister (Jack Bannon)

!!Ralph "The Birdman" Selover (Richard Marcus)
* DrivenToSuicide
* SanitySlippage

!!John Doe #12 (Tom Hulce)

!!Eve Leighton (Marian Mercer)
* TooGoodForThisSinfulEarth

!!Florence Hufnagel (Florence Halop)
* JerkAss: Mrs. Hufnagel gets passed around from doctor to doctor because of this. Even kindly Dr. Westphall pawns her off on Dr. Craig.
* ScrewPolitenessImASenior
* ShoutOut: At one point, she mentioned she and her husband used to have a diner together, [[Music/FrankZappa Flo & Eddie's]].

!!John Doe #6 (Oliver Clark)
Amnesiac patient in season 4 and 5.

!!Murray Robbin (Murray Rubin)

!!Augusta Endicott (Dorothy McGuire)
* {{Expy}}: For Rose Kennedy.

!!Brett Johnson (Kyle Secor)
* StraightGay

[[folder:Family and other outsiders]]
!!Aunt Charisse (Louise Lasser)
Dr. Ehrlich's aunt, who raised him after his parents died.
* CloudCuckooLander
* HardDrinkingPartyGirl

!!Ellen Craig (Bonnie Bartlett)
* {{Parental Substitute}}: Tends to be this to Dr. Ehrlich.

!!Stephen Craig (Scott Paulin)
* DrugsAreBad: Stephen's drug addiction causes friction with his father. His drug use is also a factor in [[spoiler: the car accident that kills him]].
* GenerationXerox: Following in his dad's footsteps by becoming a doctor.

!!Elizabeth "Lizzie" Westphall (Dana Short)
* BrattyTeenageDaughter: An aversion.
* TheCaretaker: She is this for her autistic brother Tommy, to the point where she feels guilty for going to Vassar and ends up transferring to a local school.
* DeadGuyJunior: Named for Dr. Westphall's mother, who died in a fire when he was young.

!!Tommy Westphall (Chad Allen)
* DeadGuyJunior: Named for Dr. Westphall's late father Thomas.
* VerbalTic: Due to his autism, he always refers to himself in the third person and in very simple, broken phrases. ("Tommy want cereal", "Tommy go now")
* WalkingSpoiler: Due to his role in the finale of the series.

!!Richard Clarendon (Herbert Edelman)
Union negotiator who begins a relationship with Helen Rosenthal in season 3.
* NiceGuy

!!Marcy Eisenberg (Jeannie Elias)
Helen Rosenthal's eldest child.
* CallingTheOldManOut
* TheResenter

!!Jeff Rosenthal (Ian Fried)
Helen Rosenthal's youngest child.
* MouthyKid: At one point, he calls SantaClaus an "old fairy" to his face.

!!Myra White (Karen Landry)

!!Nina Morrison (Deborah White)

!!Roberta Sloan (Jean Bruce Scott)
* ManicPixieDreamGirl

!!Katherine Auschlander (Jane Wyatt)

!!Judge Farnham (Jack Dodson)
* KilledOffForReal

!!Alex Corey (Jeff Allin)
* KilledOffForReal
* MadArtist