Everyone wanted to be the harbinger of the good news to the king.

Harbinger : a person or thing that announces or signals the approach of another.
Precursor : a person or thing that comes before another of the same kind; a forerunner.
Tender : showing gentleness, kindness, and affection.
Opponent : someone who competes with or opposes another in a contest, game, or argument.
Follower : a person who supports and admires a particular person or set of ideas.

Antonym of Harbinger is Follower