The First is a title and position given among the Jem'Hadar.
Each Jem'Hadar unit within the Dominion possesses a First who serves as its leader. Those who gain this rank are respected for their daring, skill and readiness to die for the Founders. Their scars highlights their experience in battle as well as their cunning which allows them to be good leaders despite their short lifespan. (Decipher RPG module: Aliens)