Do Min-joon is an alien who landed on Earth in 1609 during the Joseon Dynasty. He saves a girl named Seo Yi-hwa from falling off a cliff and misses his return trip to his home planet and is stranded on Earth for the next four centuries. He has a near-perfect human appearance, enhanced physical abilities involving his vision, hearing and speed, and a cynical, jaded view of human beings. Min-joon never ages and is forced to take on a new identity every ten years; he has worked as a doctor, an astronomer, a lawyer, and a banker, and is now working as a college professor.