• Choi Soo-jong as Jang Bogo/Gungbok
Jang Bogo is an historical figure who virtually dominated the seas of the East Asia (hence name "Sea God" or "Emperor of the Sea") and international trade from Tang China and Japan to the North China sea during the time of Unified Silla dynasty. Gungbok starts from lowest social class as a slave on the docks of Cheonghae. Gungbok lost his mother to pirates when he was young. His father was a slave carpenter in Police Office of Cheonghae. Working hard in the rough dock, Gungbok soon masters the sea and has the knack of building ships. Faced with challenges, he becomes calmer and bolder. Both Gungbok and his mate Nyeon learn martial arts from certain Choi Moo-chang. Such abilities helped him to rise from a gladiator to a security guard, military head of Muryongun and then ambassador of Cheonghae. As a part of this, he eliminated the pirates by installing Cheonghaejin on Wando, which is a geographically important sea route. With his clever battle strategies, he is able to defeat the army led by Madam Jami and install the true ruler of Korea. However, even after repeated requests by the king, he refuses the high positions. After the king is assassinated by the cunning Kim Yang, he prepares the army to lead a final assault and remove the corrupt ministers appointed by Kim Yang. At the end, Consul Jang Bogo is fatally stabbed in his office with a concealed knife by Yeom Jang. Jang Bogo accepts his death without any resistance, and his body is found at midnight by Nyeon, Choi Moo-chang and Jung-hwa. Even after his death, his army fights to the last man as a mark of respect.
• Chae Shi-ra as Madam Jami
A Silla noble and businesswoman. She first plays a role in Lady Jung-hwa's destiny. But as the story progresses, her grudges towards Jang Bogo leads to her downfall, and her life ends in tragedy.
• Song Il-kook as Yeom Jang/Yeom Moon
Raised by pirates, young Yeom Moon brandished short knives with remarkable skill and accuracy. Later in the story, he is captured by Jang Bogo, and receives the harshest punishment of branding as a pirate, and his forehead bears the burn mark. He is eventually released from prison by Kim Yang. For this, he trains Kim Yang's men in martial arts and leads the assault against Madam Jami's men, when they temporarily reconcile with Jang Bogo. He is later appointed the head of the king's bodyguards. With war looming against Jang Bogo, he visits Cheonghae to defuse the situation. He promises Kim Yang that if the need arises, he will assassinate him, provided Kim spares Jang Bogo's wife (daughter of Jang Bogo's trade master) and their new born child, Jung-hwa and the people of Silla. During their meeting, he tries his best to deviate Jang from his attack, but Jang has made up his mind to put an end to the ineffective and corrupt ministers in the king's council. In the end, he betrays Jang Bogo and kills him. He receives a jolt after the assassination, when Kim Yang launches an attack on Silla. Imprisoned by Kim Yang, he escapes from custody and helps Jung-hwa escape the massacre with Jang Bogo's child. He is killed by a shower of arrows fired by Kim Yang's army.
• Soo Ae as Jung-hwa
Love interest of Jang Bogo and Yeom Jang for most of the series. The mere mention of her name is enough for Jang Bogo to abandon careful consideration (which is his modus operandi) and act in a frenzied manner, without regards for the consequences.

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The series was a huge success, gaining between 28.5 and 30.0% of viewers.

2005 International Emmy Awards
• Drama series in the Asia, Africa and Middle East region - Final Round Nomination
2005 KBS Drama Awards
• Top Excellence Award, Actor: Choi Soo-jong
• Excellence Award, Actress: Soo Ae
• Excellence Award, Actor: Song Il-gook
• Popularity Award, Actor: Song Il-gook
• Best Couple Award: Song Il-gook and Soo Ae
2006 1st Seoul International Drama Awards
• Runner-up, Best Series Drama
• Best Cinematographer: Kim Seung-hwan