A General Agent is an agent, i.e., representative of another, who has a mandate of general nature.
Colonial use
In the Niger Rivers District the only Senior Agent, who administered the region (rather like a Factor) for the National African Company Limited (which was granted a charter and renamed Royal Niger Company Chartered & Limited in 1886), was promoted in 1882 to become the first of only two General Agents until it was absorbed by Southern Nigeria:
References
General Agent Wikipedia(Text) CC BY-SA