Lee Yeon-saeng is a major character in Dae Jang Geum

Dae Jang Geum

Dae Jang Geum is a 2003 epic South Korean television series directed by Lee Byung Hoon and produced by MBC. Starring Lee Young Ae, it tells the tale of an orphaned kitchen cook who went on to become the king's first female physician...

. She is the best friend of Seo Jang Geum

Seo Jang Geum

For the historical figure that this character is based on, see Jang GeumSeo Jang Geum is the main character of the Korean television series Dae Jang Geum. Based on the historical figure Jang Geum, possibly the first and only female physician of the King in all of Korean history...

. Since the first day they entered the palace as children, the two have always been there for each other. When Jang Geum is exiled to Jeju

Jeju-do

Jeju-do is the only special autonomous province of South Korea, situated on and coterminous with the country's largest island. Jeju-do lies in the Korea Strait, southwest of Jeollanam-do Province, of which it was a part before it became a separate province in 1946...

, Yeon-saeng weeps so much King Jungjong sees her and she doesn't even see him. Jungjong takes a liking for Yeon-saeng and makes her his concubine, despite Choi Seong-geum

Choi Seong-geum

Choi Seong-geum is a major character in Dae Jang Geum. She is considered the most notorious woman in the series, and is known as Lady Choi throughout much of the series...

 told him a negative remark against Yeon-saeng. When Jang Geum returns to the palace, Yeon-saeng becomes pregnant and becomes Lee Sook-won(Royal Concubine Lee)(이숙원 (李淑媛). She appoints her mentor Min Mee-geum

Min Mee-Geum

Min Mee-geumis a minor character in Dae Jang Geum. She is the mentor of Chang-ee and also second teacher to Seo Jang Geum and Lee Yeon-saeng. She first appears as a Na-in but for most of the series is a Sang-Goong. When Jang Geum and Lady Han are exiled, Choi Seong-geum casts Lady Min,...

 and other friend Chang-ee

Chang-ee

Chang-ee is a minor character in Dae Jang Geum. She is one of Jang Geum's close friends. Throughout most of the series, Chang-ee was a palace maid. She was the assistant and favorite palace maid of the Court Lady Min Mee-Geum...

 as her personal assistants.

Yeon-saeng is portrayed as a sweet and caring but emotional and physically weak young woman.

Historical Connection

For the second half of the series Yeonsaeng is known as Lee Suk-won. There was indeed a Lee Suk-won, who was one of Jungjong's consorts, who bore him 2 daughters, Princesses Jeongsun (정순옹주) and Hyojeong (효정옹주).

Trivia

The role of Lee Yeon-saeng is played by the Korean actress Park Eun-hye (박은혜 (朴恩惠)), who was originally supposed to play the role of Seo Jang Geum

Seo Jang Geum

For the historical figure that this character is based on, see Jang GeumSeo Jang Geum is the main character of the Korean television series Dae Jang Geum. Based on the historical figure Jang Geum, possibly the first and only female physician of the King in all of Korean history...

.