Anson Mount played the video game Red Dead Redemption (2010) for about a month before his audition, and he has been often told that his character bears resemblance to John Marston, the protagonist of the game.
The series portrays the events affecting the real-life characters and their actions, namely Thomas Durant, Collis Huntington, Brigham Young and Ulysses Grant with historical accuracy. Many of the schemes employed by Thomas Durant throughout the series, including manipulating stock prices in the first two seasons and misleading land investors in the fourth and fifth season actually occurred.
As a result of attacks by Native Americans, the US Army had to accompany the mobile "town" that followed the railroad crews as the Union Pacific moved west. These towns were mostly tents and wagons and not only consisted of the railroad workers, but entrepreneurs who provided services to the workers such as gambling and prostitution. "Hell on Wheels" was the actual name of the mobile tent community at that time. It was originally coined by the newspaper editor of the Springfield Republican newspaper and the name stuck.
Thor Gundersen was always referred to as "The Swede" yet he always insisted, "I am Norwegian.". However, at the time this story takes place, Norway was under the Swedish crown, and had been since 1814. So his immigration papers would have had him coming from Sweden/Norway. Norway had its own Constitution, seperate from the Swedish, but did not become independent until 1905. As many Norwegians wanted independence, it is very plausible for Gundersen to consider himself Norwegian instead of Swedish.
The character of Cullen Bohannon was loosely based on former Union General John "Jack" Casement, the real life chief engineer for the Union Pacific hired by Thomas Durant. He was later replaced by Major General Grenville Dodge but kept on as chief construction "boss" much the way Thomas Durant hired a chief engineer in season 2 but kept Cullen Bohannon on as chief construction "boss".