This is a sidebar to the Character Arc debate in Mystery Man's blog. Just some scattered thoughts I wanted to jot down before bed.
In some films, the central character does not serve to propel the story forward in a direct manner. Nor do they change. Yet they still are at the center of a dynamic story, and they are part of a mythical tradition in storytelling as valid as the Hero's Journey.
These catalytic characters fall into three main archetypes: The Fool, The Trickster, and The Messiah
Now, it is more common to find them as the antagonist (especially the Trickster, The Joker being an excellent example) - but they are sometimes used as the protagonist. And there are some cases of these characters being written with an arc, though that is not really in their nature. The story with these characters is the change they create in others.
The most obvious fool is Forrest Gump, however, not the most catalytic.
Butch and Sundance are Fools. The archetype has nothing to do with being stupid, but is of one who travels through the world on a journey, blissfully unaware of the changes/chaos they create in their passage. For Butch and Sundance, it catches up with them.
Indiana Jones is part Fool, part Trickster - and is very much the same man with the same desires and drives at the end of the first film as he was at the beginning - but he definitely triggers events, simply by being present.
Ferris Bueller: rarely has there been a better example of a Trickster catalyst in film. Absolutely drives the film, does not change, and inspires change in his friend.
Ghandi is a classic Messiah archetype. He inspires others to great change, while remaining very much the same himself. (The movie Ghandi, not to be confused with the real man, who very much changed over the course of his life.)
Captain Jack is a trickster and clearly a catalyst. Whose desires and actions drive central storyline of the Pirates trilogy? (OK, there are arguments for both Will and Elizabeth, but it's Jack's presence that gets things moving, and Jack who spurs them on.)
Another great trickster is Redford's character in The Sting, who does not himself change and yet is the catalyst for the rest of the characters to come together and to revive their old interests, and even to stretch their abilities.
Chance the Gardener in Being There is a combination Fool/Messiah, and one of the best examples of a catalytic character in film. He is clearly the protagonist, but he does not change, and is, in fact, incapable of changing. However, he triggers great change in the people who encounter him.
Powder: messiah... pretty blatantly so.
The Prestige, trickster (but is Bale the Protag? or the Antag?)
Axel in Beverly Hills Cop - Trickster
from TV: The Doctor (as in Who), Trickster
Bruce Willis in the 6th Sense was a Catalyst, but does he fit one of the above types?
Same for Poitier in To Sir with Love - arguably a Messiah, though teacher/mentor may be another archetype.
The lead in Seven Samurai... been a while, but as I remember, he starts off pretty much the same person he is throughout, but inspires other shogun to come together and protect the village.
Cool Hand Luke, again - it's been a long time. Other than accepting his fate (sacrifice), does Luke change?
McMurphy in Cuckoo's Nest?
Ethan, especially in MI 2, is portrayed as a Messianic figure.
hmmm... forgetting something that I started off wanting to talk about....
OK, need to go off to bed. Up much too late.