agent
agent - noun
an active and efficient cause; capable of producing a certain effect
a representative who acts on behalf of other persons or organizations
a substance that exerts some force or effect
a businessman who buys or sells for another in exchange for a commission
any agent or representative of a federal agency or bureau
the semantic role of the animate entity that instigates or causes the happening denoted by the verb in the clause
agent - thesaurus
broker
factor