In our social world, an agent is a person that performs some task on your behalf. This concept of agent has existed for thousands of years. For example, some Biblical laws specifically refer to agents. Three modern examples are a travel agent planning flights and accommodation for your holiday, a real-estate agent helping you buy or sell a house, and a matchmaker arranging marriages. In the recent software context, an agent is loosely a program that performs a task on your behalf. Agents have grown in popularity since the introduction of the PC (personal computer) due to the increase in complexity of the target environment for application software. Software systems must now operate robustly in a networked, global environment comprised of diverse, distributed technologies. Furthermore, the environment is dynamic, and frequent change is inevitable. Having automated help is almost a necessity.
Encyclopedia of knowledge management, second edition / David G. Schwartz and Dov Te'eni (eds.),
Vol. 1, chapter 2, pp. 12-19