centerman, n. — Green’s Dictionary of Slang

centerman n.

[prison use center, the guards’ ‘office’ in a prison wing]

(Can./US prison) a prisoner who toadies to the guards.

1970		R. Knudten Crime in a Complex Society 597: The centerman, who is identified with the staff.
1998		B.A. Owen In the Mix 5: They found little evidence for the roles of the centerman, the right guy, the merchant, the tough, and other male identities.