I must say, Il is so messed up in so many ways.
He was fanatic about the gods and Hiryuu to the point he thought everyone is just as obsessed as he is, accusing Yu-hon and Soo-won of secretly desiring Hiryuu, while all they did was hate him.
He resented and mistreated Soo-won ever since he was an innocent child, because of the conflict he had with Yu-hon, making the poor boy doubt his worth.
He made his wife a miserable, disheveled-looking shadow of a person sentencing her to years of loneliness and emotional emptiness. To think that he pathetically confessed to YON-HI in that letter that he in fact loved Kashi. Too bad she didn’t know that while all she felt was being an instrument of bringing red-haired dragon Yona to life.
He killed his own brother with a stab to the back, no matter what, it is such a low, cowardly way of doing it.
Despite Yon-hi’s pleadings of making things right between him and Soo-won to avoid tragedy and bloodshed, Il did everything to make it happen nonetheless. As if on purpose.
He knew what awaits Yona and what kind of role she has and did nothing but overprotect her, leaving her oblivious to what’s happening around, uneducated, incapable of doing anything herself and miserable in her loneliness.
He was a king that gave away lands to foreign countries and did nothing to help his anguished people or solve their countless problems.
It may result that he was doing it to fulfill or to avoid fulfilling the prophecy or something like that. That does not change his whole persona though, he was disgusting.
I still don’t get why Mundok was so loyal to him. At least Hak was a naive child when he started serving him, but Mundok? What does he know?