Main cast
- Han Hyo-joo as Dong Yi (Choi Suk-bin)
- Kim Yoo-jung as young Dong Yi
- Ji Jin-hee as King Sukjong
- Lee So-yeon as Jang Hui-bin/Jang Ok-jeong
- Bae Su-bin as Cha Chun-soo
Supporting cast
Park Ha-sun as Queen Inhyeon
- Jeong Jin-yeong as Seo Young-gi
- Jung Dong-hwan as Oh Tae-suk
- Lee Kye-in as Oh Tae-poong
- Choi Cheol-ho as Oh Yoon
- Kim Yoo-suk as Jang Hee-jae
- Son Il-kwon as Hong Tae-yoon
- Shin Guk as Do Seung-ji
- Na Sung-kyoon as Jung In-gook
- Kim Dong-yoon as Shim Woon-taek
- Park Jung-soo as Queen Myeongseong (Sukjong's mother)
- Kim Hye-sun as Court Lady Jung
- Kim So-yi as Court Lady Bong
- Ahn Yeo-jin as Court Lady Jo
- Im Sung-min as Court Lady Choi
- Jeong Yu-mi as Jung Eum
- Kang Yoo-mi as Ae Jong
- Oh Eun-ho as Shi Bi
- Han Da-min as Eun Geum
- Choi Ha-na as Mi Ji
- Lee Jung-hoon as Lee Jong-ok
- Choi Jae-ho as Park Do-soo
- Yeo Ho-min as Oh Ho-yang
- Lee Hee-do as Hwang Joo-shik
- Lee Kwang-soo as Yeong Dal
- Jung Sung-woon as Choi Dong-joo
- Jung In-ki as Kim Hwan
- Jung Ki-sung as Kim Hwan's disciple
- Lee Sook as Lady Park
- Kim Hye-jin as Seol Hee
- Choi Ran as Lady Yoon (Heebin's mother)
- Choi Soo-han as Ge Dwo-ra (Dong Yi's childhood friend)
- Jung Eun-pyo as Ge Dwo-ra's father
- Jung Sun-il as Park Doo-kyung
- Kwon Min as Cha Soo-taek
- Choi Jong-hwan as Jang Mu-yeol
- Lee Hyung-suk as Geum / Prince Yeoning
- Yoon Chan as Crown Prince, later King Gyeongjong
- Heo Yi-seul as Young Sun
- Maeng Sang-hoon as Kim Goo-sun
- Oh Yeon-seo as Queen Inwon
- Chun Ho-jin as Choi Hyo-won (cameo)
- Lee Jae-yong as Jang Ik-heon (cameo)
- Choi Il-hwa as Seo Jung-ho (cameo)
- Min Joon-hyu
 |  |  |  |  |
| Han Hyo-Joo | Ji Jin-Hee | Lee So-Yeon | Bae Soo-Bin | Jung Jin-Young |
| Choi Suk-Bin | King Suk-Jong | Jang Hee-Bin | Cha Jeon-Soo | Seo Yong-Gi |
 |  |  |  |  |
| Park Ha-Sun | Jeong Dong-Hwan | Lee Kye-In | Choi Cheol-Ho | Kim Yu-Seok |
| Wang Hu In Hyeon | Oh Tae-Suk | Oh Tae-Poong | Oh Yun | Jang Hee-Jae |
 |  |  |  |  |
| Shin Kuk | Na Seong-Kyun | Kim Dong-Yoon | Jung Sun-Il | Choi Jong-Hwan |
| government official | Jung In-Kuk | Shim Woon-Taek | eunach | Jang Moo-Yul |
 |  |  |  |  |
| Lee Hyung-Suk | Yoon Chan | Oh Yeon-Seo | Park Jung-Soo | Kim Hye-Sun |
| Lee Geum | Kyung-Jong | Queen In-Won | Queen Myeongseong | Court Lady Jung |
 |  |  |  |  |
| Kim So-Yi | Ahn Yeo-Jin | Lim Seong-Min | Jung Yoo-Mi | Kang Yu-Mi |
| Court Lady Bong | Court Lady Jo | Court Lady Yoo | Jung-Im | Ae-Jong |
 |  |  |  |  |
| Oh Eun-Ho | Han Da-Min | Lee Jeong-Hun | Choi Jae-Ho | Yeo Ho-Min |
| Si-Bi | Eun-Geum | Lee Jong-Wook | Park Do-Soo | Oh Ho-Yang |
 |  |  |  |  |
| Lee Hee-Do | Lee Kwang-Soo | Cheon Ho-Jin | Jung Sung-Woon | Lee Jae-Yong |
| Hwang Joo-Sik | Young-Dal | Choi Hyo-Won | Choi Dong-Ju | Jang Ik-Hyun |
 |  |  |  |  |
| Jeong In-Gi | Choi Ran | Lee Suk | Kim Hye-Jin | Jung Eun-Pyo |
| Kim Hwan | Hee-bin's mother | Lady Park | Sul-Hee | Ge Dwo Ra's father |
 |  |  |  |  |
| Son Il-Kwon | Choi Su-Han | Yeo Hyeon-Soo | Maeng Sang-Hun | Kim You-Jung |
| Hong Tae-Yoon | Ge Dwo Ra (young) | Ge Dwo Ra | Kim Goo-Sun | Suk-bin (child) |