The agents (aka King's agents) are the Agents of the King of Daventry.
Behind the scenesEdit
The 'agents' only are mentioned in PCJR version of King's Quest (and possibly other early 1984 versions) if Graham tries to leave the castle after Edward's death. In 1987 version this message does not appear, though its still in the game files.
Additionally there is a reference to the King's agents in an easter egg (cut from the game) found in the script files, in which Graham could have tried to find a 'flamethrower' and attempted to use it on Edward, only leading to his death to be torched at dawn.
In mideval terms the agents are very similar to the ministers and stewards, including the prime minister or seneschel of the kingdom. But in this case it may be referring to the 'guards', or a special security detail (similar to royal guard?).