[1] He is characterized as a competent and compassionate doctor who tries to do what he thinks is best for his patient but his single-minded stubbornness has sometimes clouded his judgment, such as when he insists on a particular course of action that is contrary to both advice and evidence.
Charge Nurse Maggie Lockwood, who sometimes uses the nickname "Big Red" when referring to Dr. Halstead, once described him as "a slightly anal, overly stubborn, rule breaking, control freak".
In season 1 Dr. Halstead clashes a number of times with Dr. Connor Rhodes, a trauma surgery fellow, and Sharon Goodwin, the chief administrator, over hospital practices and policies.
He also earns the ire of attending Dr. Kendra Perrington in the episode "Inheritance" for overriding her at the request of the patient's brother, who was his former schoolmate, only to find out that she was on the hiring committee.
He eventually decided to move on and starts dating pathologist Nina Shore (portrayed by Patti Murin, the real-life wife of Gehlfuss' co-star Colin Donnell).
In season 4 they prepare for their wedding but Dr. Halstead finds himself in a difficult position when a neighborhood friend he made a house call to turns out to be federally listed criminal wanted by both the CPD and FBI.
[9] Will attended De La Salle Institute, where he excelled academically but was also bullied by the more popular students and given the derogatory nickname "Ginger Spice".
She discovers that she enjoys interacting with patients and learning about the psychological side of medicine, although it leads her to subconsciously "shrink" her own colleagues, much to the nurses' amusement.
[17] Dr. Rhodes attended Universidad Autónoma de Guadalajara in Mexico and spent a year in Riyadh, Saudi Arabia following his residency.
Dr. Rhodes comes from a wealthy background and was written as a "local boy" who left Chicago to escape his family before returning many years later.
He was in a relationship with attending surgeon Dr. Samantha "Sam" Zanetti but they break up in the episode "Saint" when she takes a job at Johns Hopkins in Baltimore.
[8] Robin develops health problems that cause difficulties in their relationship; she begins behaving erratically, and it's discovered that she has a brain tumor.
In Season 4, Rhodes is about to leave to take a job at the Mayo Clinic when he is offered the opportunity to run Med's newly-developing hybrid operating room in the hospital's emergency department.
He decides to take the job at Med, not knowing that the hybrid OR was funded primarily by an anonymous donation from his father, and was solicited by Dr. Bekker.
When the failed operation is revealed to be due to a faulty implant, Connor briefly considers that he may have been wrong; however his father's sudden death by an insulin overdose, and Bekker's subsequent behaviour, leads him to believe that she is the killer.
In season 5, after the deaths of both his father and Bekker, who committed suicide after admitting to killing Cornelius in an attempt to win him back, Connor leaves Chicago to have a fresh start.
Lieutenant Commander Dr. Ethan Choi, USNR, is the former Chief of Emergency Medicine and a former active duty United States Navy officer.
[18] His aloof and detached exterior sometimes intimidates the medical students and junior residents under him, but he is shown to be sympathetic and supportive with them, as well as his other coworkers and the CFD paramedics.
He is of Korean descent[20] (like actor Brian Tee) and once implies that he had been subjected to racism during his childhood since he grew up in a neighborhood where there were "not many families with the last name Choi".
Beginning in season 2, he takes over from Dr. Halstead as Chief Resident[22] and has an unforgettable first day, much to everyone's amusement because they are used to seeing him calm and in control.
Eventually, he seeks proper treatment after breaking down in Dr. Charles' office but uses his work as an excuse to put off subsequent counseling sessions.
[5] After a series of emotional near-breakdowns and a heated confrontation with a patient's father, he resumes counselling and joins a support group at the VA.[15] He adopts a parrot who refuses to fly due to trauma from being verbally abused and being cooped up in a hoarder's house for months.
[2] In the season 5 episode "I Can’t Imagine the Future", he is recalled by the Navy to cover for an aircraft carrier medical officer who had fallen ill and would be deployed for two months.
He lived with his then girlfriend Dr. Vicky Glass (Cynthia Addai-Robinson), who works at the nearby VA hospital and is a fellow Navy veteran.
Her first love had been photojournalist Reggie Dixon when she was an eighteen-year-old high school graduate but she chose to attend college rather than travel the world with him on his assignments.
A well-respected veteran psychiatrist at Chicago Med, Dr. Charles combines his human touch with instinct and intuition to diagnose patients.
Margaret "Maggie" Lockwood is the charge nurse of the Emergency Department and runs a tight ship with a firm hand and a quick-witted sense of humor.
In the episode "Natural History", it is revealed that she comes from a large and close-knit extended family and has a sister, Denise who was male at birth, had gender confirmation surgery and moved to Dallas, Texas.
Rhodes becomes convinced that Bekker has deliberately manipulated events to ensure that the pair remain involved in each other's lives, although it appears throughout the season that he is simply paranoid, with all incidents having innocent explanations.
Dr. Crockett Marcel is introduced as a Fourth Year Resident/later an Attending Physician in General Surgery who eventually replaces Dr. Connor Rhodes after he resigns from Med for a fresh start.