The man who folded himself

This classic work of science fiction is widely considered to be the ultimate time-travel novel. When Daniel Eakins inherits a time machine, he soon realizes that he has enormous power to shape the course of history. He can foil terrorists, prevent assassinations, or just make some fast money at the racetrack. And if he doesn't like the results of the change, he can simply go back in time and talk himself out of making it! But Dan soon finds that there are limits to his powers and forces beyond his control.

David Gerrold is an American science fiction screenwriter and novelist, known for his script for the popular original Star Trek episode "The Trouble With Tribbles", for creating the Sleestak race on the TV series Land of the Lost, and for his novelette "The Martian Child", which won both Hugo and Nebula awards, and was adapted into a 2007 film starring John Cusack. - Wikipedia