In Ray Bradbury's short story "A Sound of Thunder," Eckels joins a time-traveling team to hunt a tyrannosaurus Rex. During the hunt, he steps on and kills a butterfly. When he returns back to the present day, he finds that his actions have caused an alternate present.
The original plan was for Eckels to shoot a tyrannosaurus Rex that was dying, which would minimize the effects of changing the present, but the dinosaur scares Eckels, which leads to the accidental squashing of the butterfly. Once the hunter and the team return to the present, the changes observed are that the spelling of English words has changed and that a dictator-like candidate won the presidential election. In response to the changes, the team leader, Travis, kills Eckels.
The term butterfly effect as it relates to time travel is attributed to this story. This effect is the idea that even the smallest change in the past would have extensive repercussions for many present and future events.
Ray Bradbury wrote "A Sound of Thunder" in 1952. Among his most famous works are "Fahrenheit 451" and "Something Wicked This Way Comes" and "The Martian Chronicles." Bradbury died in 2012. He was 91 years old.