Ray Bradbury's science fiction short story "A Sound of Thunder" has a plot driven by the actions of the characters:
This character certainly is the catalyst to the problem of the plot of Bradbury's story. Were it not for Eckels's stepping off the path where he has been forbidden to do so and bringing back the crushed butterfly on his boot, the alterations in life in the present time would not have happened--the "butterfly effect."
Travis is the safari guide into the past who takes Eckels on his trip to shoot a Tyrannosaurus Rex in the Time Machine. He describes the dangers of the time travel and of shooting a dinosaur to Eckels, who accuses Travis of attempting to frighten him. Travis replies that he is doing so in an attempt to prevent anyone from going who will disrupt the order of things or cost people their lives.
When Eckels does get frightened, it is up to Travis to shoot the dinosaur and make Eckels remove the bullets so that nothing will be out of order in the past.
Interestingly, this character's name means "hope." Working for the time-travel company, he scouts ahead for animals that will not have a future, and, therefore, have no part in any order of the future. For instance, he has found a Tyrannosaurus Rex who will be killed by a falling tree; this is the dinosaur that Eckels is assigned to shoot. If Eckels kills this dinosaur, nothing in the future will change.