If a verb is in the passive voice, the subject of the sentence is not the "doer" of the action of the verb (e.g., "The man was bitten"). To indicate the agent of the action of the verb, English adds a phrase like "by the dog" ("The man was bitten by the dog"). Greek simply uses the preposition hypo and the genitive case of the noun or pronoun for the agent or "doer' of the action. English uses the preposition "by"—without a preposition.

The agent is the one who generates the action of a passive voice verb. Put the agent in the genitive case.