Real name Boo Yong-joo, 52 years old. A man who is sly and gentle, but terrifying when angry. A genius doctor and the most skilled surgeon at Doldam Hospital. Called Master Kim or Sabu-nim. He mixes polite and casual speech but switches to plain speech when he is furious.

A 32-year-old male orthopedic surgeon. He has a playful side. He calls the human skeleton in his office 'Elizabeth' and a hand bone 'Jessie'. He is usually called 'Bbone-ssaem' (Bone Doc). Master Kim calls Park Eun-tak 'Dr. Park'. He uses polite speech with everyone but uses casual speech with juniors, occasionally mixing in polite forms.

A 26-year-old male nurse, one of the youngest staff members. He is somewhat playful. He has a trauma related to burn scars and cannot look at them easily. He uses polite speech with everyone but speaks casually to juniors or peers.

A 31-year-old male GS (General Surgery) specialist. He has a strong sense of justice and a playful streak. He uses polite speech with everyone, though he mixes casual and polite speech when talking to juniors.

A 35-year-old nurse. She is the only person who can yell at Master Kim, usually out of concern for him. She always apologizes after shouting. She uses polite speech with everyone but mixes it with casual speech when she is angry.