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.