The show has adopted a new programming format in which a one-hour conventional TV episode is spliced into two half-hour broadcasts with ads inserted in the middle.

KBS 2TV's crime thriller-comedy "Queen of Mystery," which was at No. 1 before the arrival of "Ruler," stood at 9.2 percent, while episodes three and four of SBS TV's new show "Suspicious Partner" clocked in at 6.1 percent and 7.2 percent, respectively.

"Ruler" is a show about a crown prince named Lee Seon of the Joseon Dynasty (1392-1910) -- played by rising star actor Yoo Seung-ho -- who has been raised wearing a mask since infancy to conceal his identity due to mysterious circumstances.

He wages a war against a technocratic guild known as "Pyeonsoohoe," which seeks to privatize the public water supply for personal gain.

Former child actress Kim So-hyun plays the crown prince's love interest Han Ga-eun and L of boy band Infinite is cast as the prince's confidant peasant. Veteran actor Huh Joon-ho stars as the main antagonist Daemok, who heads the Pyeonsoohoe. (Yonhap)