Agent

Agent is a generalized semantic or thematic role. The agent of an event is the entity that brings about an event and has control over it.

The Agent role has a 'privileged' status in many languages. In accusative languages, it is typically encoded as a subject (in the nominative case); in ergative languages, it is associated with a special case, the ergative. Irrespective of the alignment system of a language, the Agent role is plays a crucial role in various syntactic constructions, e.g. specific types of control structures and imperatives.

Example
In the following examples Miguel is the Agent:


 * 1)  Miguel chased Gianni.
 * 2)  Miguel gave Pedro some water.
 * 3)  Pedro was hit by Miguel. (passive voice)

Other languages

 * German Agens
 * Russian агенс

Link
Utrecht Lexicon of Linguistics