Complex sentence: Lee Gyeom (Lee Joon-gi) is the son of a virtuous nobleman Lee Won-ho, a trustworthy supporter and brother to the king and a central member of the secret organization Cheonwoohoe, composed of important nobles and with the king as their leader.
Split into simpler sentences: Lee Gyeom (Lee Joon-gi) was the son of a virtuous nobleman Lee Won-ho, who the king's trustworthy supporter and brother. He was also a central member of the secret organization Cheonwoohoe, composed of important nobles with the king as their leader.