In a classic role-playing game there are two types of roles Game/Dungeon Masters and Players. That does lead to a lot of work, responsibility, creativity as well as power, let’s call it agency, for one person. Upon further examination there are really more roles that are sometimes unspoken and assumed that can be divided in the following:
Demiurge
Creates the world and the laws of nature that govern in. In many cases that can be deferred to source material, be it the works of J.R.R. Tolkien (The Lord of the Rings), Robert E. Howard (Conan, Solomon Kane, …) or a world of your own invention.
Director (Narrator)
Similar to what a director would do with a camera in a movie, establishes the focus and perspective of the scene, which s/he. Decides who the spotlight is on, as well as what actions, activities, topics, etc …
Fate/Story (Future)
Establishes Theme, Mood, drives the story forward, puts people and places together. This is the overarching as well as the individual Characters decisions who’s agency is part of this Is this the player role? But also the Antagonist (be it person, environment, …) Sometimes we know the end but not how we got there and have to work in reverse That could be true for conflict resolution as well.
Chronicler (Past)
Records the facts that have been established, as well as by whom.
Arbiter/Judge
The person or whose judgment or opinion is considered authoritative
It’s possible to have a lot or all the roles in on player, but more likely then not it would make sense to divide them for greater enjoyment and involvement of everyone.