[n] the semantic role of the animate entity that instigates or causes the hapening denoted by the verb in the clause
[n] an active and efficient cause; capable of producing a certain effect; "their research uncovered new disease agents"
[n] a businessman who buys or sells for another in exchange for a commission
[n] a representative who acts on behalf of other persons or organizations
[n] any agent or representative of a federal agency or bureau
[n] a substance that exerts some force or effect