The Doctor is a character in Harvest Moon GBC 2.
He will do a checkup for free when you visit him at the clinic. He can always be found at the clinic.
He and Nancy arrive in the Spring of the second year. The two work at the clinic together. The Doctor can assess your character's energy levels and health. If you're sick, you will need to spend the remainder of the day and night at the clinic, and you will be released the next morning.
He and Nancy have an event where the player becomes almost deaf if the player plays past the third year.