|Birth place:||Wicklow County, Ireland|
|Behind the scenes|
|Portrayed by:||Ben Esler|
|Seasons:||1, 2, 3|
|Last episode:||"It Happened in Boston"|
|Appearances:||28 episodes (see below)|
Sean is from County Wicklow, Ireland and his mother and three of his brothers still remain in County Wicklow. His mother placed him and Mickey on a boat in Cork. His father worked the land in Ireland and is now deceased. He claims he only has eight toes.
When he and Mickey were children, they stowed away on the Dublin Special, never feeling so free in all their lives. Mickey gives this experience to Thomas Durant as the reason that he and Sean join the Union Pacific Railroad.
While living in Boston, Mickey and Sean had some trouble, though they do not speak of the incident without great reluctance, especially on Mickey's part. Once, when Sean pressed Mickey about Boston, he blurted "I didn't mean to kill her". Two women in Boston were strangled, a school teacher and a shopgirl, both which were ultimately blamed on Sean. ("Pilot", "A New Birth of Freedom", "Viva La Mexico", "It Happened in Boston")
- Main article: Season 1
Sean and Mickey take a westbound train, reading a newspaper story about a Union soldiers' murder in Washington D.C. and meeting Cullen Bohannon, the murderer, though no one knows this. As it turns out, all three men are headed to the Hell on Wheels railroad construction site. On arrival the two brothers establish a nostalgic picture show business. ("Pilot")
As it becomes clear that the McGinnes Brothers' magic lantern show is a great commercial success, Thor Gundersen turns up to extort money for his "protection". Sean and Mickey are forced to decide between paying off Gundersen and keeping their ideal location between "the liquor and the whores" and refusing to pay and moving next to the slaughterhouse. ("Immoral Mathematics")
- Main article: Season 2
Sean now sells plots of land under the supervision of Thomas Durant. Lily Bell is horrified when he attempts to make money from the refuges from Durant, Nebraska though Sean sees little problem with the arrangement. ("Durant, Nebraska")
Sean also turns his attentions to Ruth. Hoping to win her affection, he agrees to be baptized; however, when he kisses her, she pushes him away. Later, he waits in Ruth's tent, drunk. The next day, Sean goes to Ruth to apologize for his actions and speaks to her about marriage. Ruth refuses outright, telling him she could never marry a Catholic. ("Blood Moon Rising")
- Main article: Season 3
Sean begins to secretly work for Durant, feeding him information about Bohannon and assisting in undermining the railroad's progress. Bohannon makes it clear on several occasions that he knows about Sean's new working relationship with Durant, which makes Sean very nervous.
Sean gets mixed up in a murder when he walks in on Durant immediately after he kills Senator Nathan Metcalf. Sean takes the murder weapon, a gun, from Durant. Terrified, Sean convinces Mickey to help him make the body disappear, which Mickey reluctantly does, though he tells Sean he never wants to see him again. ("Cholera")
A lawman from Boston comes to investigate the disappearance of Senator Metcalf, causing Sean to panic. He approaches Mickey for help again but his brother turns him away, saying he is dead to him. Distraught, Sean thinks of leaving Hell on Wheels, but decides against it, especially when the lawman telegraphs Sean's name back to Boston. He confronts Mickey again, telling him he will go to Ruth to confess and then turn himself in, though Mickey reminds him that will also implicate his brother and that Sean will hang. Tired of running, Sean ignores his advice and goes to Ruth to confess. Sean, truly attempting to confess is rebuffed by Ruth, due to his previous unwanted advances. He begins to tell her a story about two girls that he and Mickey met in Boston. He implies that Mickey is not the person he seems. He is cut short by a bullet from Mickey, who hid in the curtains behind the altar. Sean dies in Ruth's arms and is buried by Bohannon and Mickey. ("It Happened in Boston")
- Main article: Ruth Cole
Sean took a shine to Ruth in season 2, though at first he was merely friendly. He began to attempt to win her affection, proposing marriage several times and giving her a Claddagh ring as a token of his affection. Ruth refused him each time, though he continued to pursue her. After each rejection, Sean became more and more persistent, once appearing in Ruth's tent after nightfall, drunk and angry. Sean attempted to appease Ruth's objection to his Catholic faith and was baptized by her, though this was not enough for her to accept another marriage proposal. This enrages Sean further, especially after he discovers Ruth's intimate relationship with Joseph Black Moon.
Prior to his death, Sean was cold and rude to Ruth, though he does attempt to tell her the truth about himself and Mickey in Boston.
|Season 1 appearances|
|"Pilot"||"Immoral Mathematics"||"A New Birth of Freedom"||"Jamais Je Ne T'oublierai"||"Bread and Circuses"|
|"Pride, Pomp and Circumstance"||"Revelations"||"Derailed"||"Timshel"||"God of Chaos"|
|Season 2 appearances|
|"Viva La Mexico"||"Durant, Nebraska"||"Slaughterhouse"||"Scabs"||"The Railroad Job"|
|"Purged Away with Blood"||"The White Spirit"||"The Lord's Day"||"Blood Moon"||"Blood Moon Rising"|
|Season 3 appearances|
|"Big Bad Wolf"||"Eminent Domain"||"Range War"||"The Game"||"Searchers"|
|"One Less Mule"||"Cholera"||"It Happened in Boston"||"Fathers and Sins" *||"Get Behind the Mule" *|