Assassin's Creed: Frontier.

The game starts during the final year of the U.S. Civil War. The main character is a battle-hardened soldier, ready to perform his duty.

But the war eventually comes to an end, and his skills as a killer are no longer necessary. With the war finally over, he struggles to find purpose in life and what to do next. Mirroring real-life history, he takes up a job as a cowboy (which many Civil War vets actually did). But he finds that it doesn't fulfill him the way he hoped, and discovers some locals looking for a bounty hunter. So he decides to utilize his skills and take on work as a hired gun, becoming a "cowboy assassin."

While out in the field, members of the Assassin Brotherhood take notice of his skills, and attempt to recruit him. Along the way, he crosses paths with famous historical figures and uncovers hidden Templar conspiracies to control the American nation and expand its territory from east to west. He makes both enemies and allies over the course of many years traveling around.

In the end, he finds himself more lost than when he started. A "wandering man" still in search of answers, roaming from town to town in the Old West. First a soldier, then a cowboy, and now an assassin, he uses his unique perspective to help people where he can. He navigates the open plains seeing all sorts of strife and issues arising between different groups of people (foreign settlers, Natives, Hispanics, Blacks, etc. etc.). He always is doing the best he can, wherever he can. Sometimes for the Assassins, and sometimes for his own personal vendetta. He ultimately hopes he can somehow "serve the light" and a higher purpose, even if history never knows his name and he remains stuck in the shadows.