This label is for a role introduced by certain constructions (e.g., causative constructions) in which an event that ordinarily has a certain set of core participants (possibly including a Force or Agent) is framed as caused by another participant via valency-augmentation.
In English, this is rarely expressed with a preposition, but may be seen in the passive by-phrase of a Caused Motion Construction:
Note that in the example, the horse is the one actually jumping, and (if annotated) would thus be the Agent; whereas Claire is the Causer of that semi-volitional jumping event.
A Causer may be animate or inanimate.
Prior to v2.6, "Causer" had a different meaning which is now termed Force.
External instigator of an event.