Main •
Lee Joon-gi as Kim Sung-yeol ("Night Scholar") :A loyal and courageous scholar who is a close friend of Crown Prince Jonghyun. He turns into a vengeful vampire following the deaths of his family and friend. •
Lee Yu-bi as Jo Yang-sun/Seo Jin :A cheerful and kind bookseller, who goes around dressed as a man in order to earn money for her family. She is the direct descendant of Gwi from her mother's side. •
Shim Chang-min as Crown Prince Lee Yoon :The son of Crown Prince Sadong. He seeks to take revenge on Gwi, who was responsible for the death of his father. •
Lee Soo-hyuk as Gwi :A bloodthirsty and evil vampire who wishes to rule over humans, who likes Choi Hye-ryung. •
Kim So-eun as Lee Myung-hee/Choi Hye-ryung (another character after 120 yrs) :Sung-yeol's first love and fiancée. She was deeply in love with Sung-yeol and she gave her life to save Sung-yeol. :Choi Hye-ryung is the daughter of the prime minister, who resembles Lee Myung and serves Gwi. She secretly falls in love with Prince Lee Yoon as she is striving to become Joseon's Queen as a revenge for her father.
Supporting People around Sung-yeol •
Jang Hee-jin as Soo-hyang :The head of Hwayang-gak and one of Sung-yeol's confidant. She has a one-sided love for him since he was her savior. •
Choi Tae-hwan as Ho-jin :Sung-yeol's confidant and head of the household. •
Kwon Hwa-woon as Hyun-gyu
People around Lee Yoon •
Yeo Eui-joo as Noh Hak-yong :A
Sungkyunkwan scholar and close friend of Lee Yoon. •
Han Jung-soo as Baek In-ho :Lee Yoon's martial arts teacher and personal guard. He is also a best friend of Crown Prince Sadong. •
Lee Soon-jae as King Hyeonjo :Lee Yoon's grandfather •
Jang Seung-jo as Crown Prince Sadong :Lee Yoon's father. He was killed by Gwi when he attempted to find the secret to kill Gwi to stop the Gwi's puppet king monarchy
People around Yang-sun • Jung Gyu-soo as Jo-saeng :Yang-sun's foster father. He is sick and unable to work to support his family. He is the keeper of Crown Prince Jonghyun's memorandum. •
Oh Yoon-hong as Kkot-boon :Yang-sun's foster mother • Park So-young as Dam-yi :Yang Sun's sister. She is unable to walk.
Court officials • Son Jong-hak as Choi Chul-joong :The
prime minister who is the main opposer to the King and Crown Prince. He is the father of Hye-ryung. •
Kim Myung-gon as Noh Chang-sun :The chief left minister who supports the King and is one of his close confidants. He is the grandfather of Hak-yong. • Kim Jong-goo :The defense minister who is the prime minister's associate.
Special appearances •
Lee Hyun-woo as Crown Prince Jonghyun (cameo, episode 1) :The original "Lustful Student", who wanted to get rid of Gwi, but was killed in the process. •
Yang Ik-june as Hae-seo (cameo, episode 1) :The Guardian Gwi. • Han Ji-woo as Royal Concubine Kim (cameo, episode 1) •
Park Ji-il as Kim Sung-yeol's father (cameo, episode 1) •
Kim Ye-ryeong as Kim Sung-yeol's mother (cameo, episode 1) • Lee Ho-jae as King Moonjo, Crown Prince Jonghyun's father. (cameo, episode 1) ==Production==