I thought I would see what Wikipedia has to say.
Its entry on Agency (sociology) opens with this:
In
social science,
agency is defined as the capacity of individuals to act independently and to make their own free choices. By contrast,
structure are those factors of influence (such as social class, religion, gender, ethnicity, ability, customs, etc.) that determine or limit an agent and their decisions.
That is consistent with how I teach theoretical sociology. It has no real connection to this thread - no one here is talking about
agency vs structure, or related matters like
Weber vs Marx. The discussion is about the much more common-sense notion of
how much the player is able to influence the play of the game. And given that the crux of the games being discussed - ie RPGing - is shared imagining, the discussion is particularly focused on
how much the player is able to contribute to and shape that shared imagining.
That entry has a number of "see also" links, but neither it nor any of them seem to deal with literature.
There is
an entry on Character (arts), which opens "In
fiction, a
character (sometimes known as a
fictional character) is a
person or other being in a
narrative". That seems common sensical enough. But there is no occurrence in that entry of the word "agency". At the end of the opening paragraphs we are told "The relation between characters and the action of the story shifts historically, often
miming shifts in society and its ideas about human
individuality,
self-determination, and the
social order." Later on there is a discussion of Aristotle's distinction between
qualities and
actions.
I don't think there are that many RPGs that try to say anything meaningful about the relationship between human individuality and the social order. HeroWars/Quest played in Glorantha might be one. In Classic Traveller characters have a Social Standing stat, and in our game that can be a factor in influence checks, including when they have been used to solve disputes among the players, I guess that says something, though it's not super-profound. The original Oriental Adventures tried to make something similar a part of the game, although the execution falls a bit short of the ambition.
When I think of RPGs that try to tackle the issue of qualities vs actions, the first that comes to mind is Burning Wheel, in part because qualities (Beliefs, Instinct, Traits) can all be changed, and changes in Traits are governed by the Trait Vote which is meant to have regard to actions performed. Likewise actions performed which resolve certain Beliefs are one major trigger for writing new ones.
I don't think D&D has ever tried to tackle either of these issues: with the exception (noted above) of OA, it conveys no sense of social order beyond a bit of set dressing; and there are almost no cases where the qualities of PCs are connected to actions (falling from paladinhood is the only - notorious - exception that comes to mind).
So I'm still at a bit of a loss as to how literary notions of agency bear upon RPGing in general.