who are the characters featured in this series?
Do Min-joon and Cheon Song-yi are two of them.
My Love from the Star
Do Min-joon (Kim Soo-hyun) is an alien that landed on Earth in the year 1609, during the Joseon Dynasty. As he saves a young girl named Yi-hwa from falling off a cliff, he misses his trip back to his planet and is stranded on Earth for the next four centuries. He possesses a near-perfect human appearance, enhanced physical abilities involving his vision, hearing and speed, and a cynical, jaded view regarding human beings. As he never ages, Min-joon is forced to take on a new identity every ten years, having been a doctor, astronomer, lawyer, and banker, and now presently working as a college professor.

Cheon Song-yi (Jun Ji-hyun) is a famous Hallyu actress, having attained stardom since middle school, however her haughty demeanor has earned derision in the entertainment industry and social media. 
my love from the star season 1 episode 7 UNANSWERABLE what is 'my love from the star'? It is a South Korean romantic fantasy television series.
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My Love from the Star [SEP] Synopsis
Do Min-joon (Kim Soo-hyun) is an alien that landed on Earth in the year 1609, during the Joseon Dynasty. As he saves a young girl named Yi-hwa from falling off a cliff, he misses his trip back to his planet and is stranded on Earth for the next four centuries. He possesses a near-perfect human appearance, enhanced physical abilities involving his vision, hearing and speed, and a cynical, jaded view regarding human beings. As he never ages, Min-joon is forced to take on a new identity every ten years, having been a doctor, astronomer, lawyer, and banker, and now presently working as a college professor.