And this is just the beginning, get ready for a roller coaster ride. 😎

Well, to start off, that isn't a spoiler. His father does not appear in the same setting or near Sung Jin woo until the end of the story, in fact, his father has no relation to the story at all during this arc or any arc afterwards. In other words, the spoiler tag isn't needed.

This is for anyone wondering why he's being called "king" by the architect:

The Shadow Monarch, Osborne (aka. The Sovereign of Death) wanted to use Sung Jin woo as his human vessel because the Spirtual beings (Monarchs and Rulers, the enemy of the Monarchs) has the ability to do so (The Nation Level hunters had a relation to this).

The reason why the Shadow Monarch wanted Sung Jin woo specifically is because he took interest in Jin woo after narrowly avoiding death in any situation, especially in those years as a hunter, while he was still the "Weakest hunter".

Problem is, any vessel the Shadow Monarch wanted to use could never handle his awesome power (The Shadow Monarch was one of the Strongest Monarchs), and eventually perished because of it.

This is why the Shadow Monarch made a deal with the Architect to find him a suitable vessel, to which the Shadow Monarch would reward the Architect with power. He trained Sung Jin woo with the system and the quests, along with the daily challenges to make him suitable enough to handle his power. Every odd quest (The forceful killing of enemies, the Key which was provided for this gate, etc.), the Job change, the system, everything was planned mostly by the Architect and The Shadow Monarch to make Sung Jin woo a person with enough power for the Shadow Monarch to possess Sung Jin woo.

I won't continue onwards because everything else will probably be revealed later, and once the necessary chapter is released I may create another spoiler comment similar to this.