Main cast

• Kwon Sang-woo as Park Tae-shin

A 35-years old genius thoracic surgeon who is misunderstood due to his straightforward manner of speaking, but is kind and soft-hearted.^[2][3] Sometimes he acts impulsively, once he even pushed Seo out of his way, when helping ill waitress. Previously he worked in the USA. Dr. Park grew up in an orphange, where he was abused, along with other children, by director. Later Park was adopted. After many years he tried to find his biological parents, but eventually gave up. Later he developed romantic interest in Ah-jin.

• Jung Ryeo-won as Seo Joo-young

A charismatic and ambitious thoracic surgeon.^[4] Lee Min-jung and Lee Na-young were previously in talks for the role.^[5][6] Sometimes professor Seo feels discriminated due to being female surgeon, so she always tries her best. She also got her medical research supported by Research Centre. Joo-young is in relationship with Seung-jae. At the beginning of the series Seo had some eating disorders, but eventually overcome these.

• Ju Ji-hoon as Han Seung-jae

A renowned 36-years old internist and the youngest chief, whose mild-mannered appearance hides his heart-of-ice interior (though it is later revealed that he actually is quite sensitive person). He is the leader of top team and son of chairman of the Gwang Hae University Hospital, Lee Doo-kyung.^[7] As illegitimate child (in Korea children usually inherit the father's family name), he was raised by single mother, who eventually died due to severe pancreatitis, leaving Seung-jae devastated. Chief Han has had feelings for professor Seo ever since medical school. The two eventually started seeing each other. By the end of the series he is appointed as chairman of Kwanghye University's second hospital.

• Oh Yeon-seo as Choi Ah-jin

An enthusiastic and energetic resident surgeon who has been in the field for only two years. She is close friends with Kim Seong-woo,^[8] but fell in love with Tae-shin. Ah-jin used to be a big eater, which eventually lead her to have kidney stones. Later she was diagnosed with Multiple endocrine neoplasia type 1 (MEN1) and was involved in clinical trials.

• Choi Min-ho as Kim Seong-woo

A good-natured resident surgeon, and the youngest member of the team. He has a one-sided crush on Choi Ah-jin.^[9] When she was hospitalised he even pretended to be her boyfriend, in order to be allowed to visit her. Seong-woo had very hard moments, when he had to pronounce death of his school junior (who used to have a crush on him).

Supporting cast

• Kim Young-ae as Shin Hye-soo - The deputy director of the Gwang Hae University Hospital.^[10] She has been manipulating younger doctors, especially dr. Park, prof. Seo and chief Han, in order to have Royal Medical Centre opened. She is chairman's daughter in law (although divorced with his son). It's later revealed that she suffers from vascular dementia. Shin also had a son, who she gave up. Then the son died, before the two could reunite.
• Ahn Nae-sang as Jang Yong-seop - Chief of surgery.^[11] He wants to control professor Seo, but is not always obeyed.
• Park Won-sang as Jo Joon-hyuk - A kind 43-years old anesthesiologist at the hospital idolized by Ah-jin.^[12]
• Lee Hee-jin as Yoo Hye-ran - The sociable surgical nurse of the team who is supportive of Park Tae-shin.^[11]
• Alex Chu as Bae Sang-kyu - A kind-hearted 34-years old medical imaging specialist of the team who hides great ambition.^[11][13]
• Kim Ki-bang as Jung Hoon-min - A 34-years old neurosurgeon of the team who is in a relationship with Yeo Min-ji.^[14]
• Jo Woo-ri as Yeo Min-ji - Another surgical nurse of the team who is the love interest of both Bae Sang-kyu and Jung Hoon-min.^[11][15]
• Kim Sung-kyum as Lee Doo-kyung - Chairman of the Gwang Hae University Hospital and the father of Han Seung-jae, who he treats as a mistake, despite young doctor's many achievements. Apart from chief Han, he has at least two legitimate sons, however neighter of them appeared on screen. As chairman Lee falls ill, most of his responsibilities are taken over by deputy director Shin.
• Lee Dae-yeon as Hwang Cheol-goo - The director of the Paran Clinic.^[16]
• Jo Woo-jin as Doctor Lim.
• Kim Cheong as Han Eun-Sook - Mother of Han Seung-jae. She was abandoned by chairman Lee (probably when still pregnant), thus raised Seung-jae under her family name. She has always been very proud of her son and wanted to protect him from suffering. Eun-Sook suffered from alcoholism and eventually died of acute pancreatitis in her son's arms. Her last wish was Joo-young and Seung-jae be together, and they did.
• Kal So-won as Eun Ba-Wi - Patient of the hospital. She is very close with dr. Park. Ba-Wi went through bone marrow, and then lung transplant. She lived in orphanage until her biological mother was found.
• Lee Do-Kyung as orphanage director.