Growing up the son of a poor Catholic/Nationalist clerk in the mostly Unionist/Protestant town of Coleraine, Ireland, Sleater found the pressure of small town life unsuited to his knack for adventure and organization.
Prior to the Irish War of Independence, Sleater worked as a cattle inspector in Coleraine ("Ourselves Alone"). At 17 he volunteered to fight the British, but was turned down twice by Sinn Fein politician John McGarrigle ("Battle of the Century"). Owen's nationalist instincts and talent for organisation and skills that included marksmanship, explosives and political subversion propelled him to join the Irish Republican Army, then fighting a War of Independence (1919-1921) against the British in order to procure a United Irish Republic. Later he worked as an advance man for McGarrigle and was responsible for ensuring his safety on a fundraising trip around America in the winter of 1920-1921, that took them to New York, Boston and Chicago before recalling on Atlantic City ("Ourselves Alone").
- Main article: Owen Sleater Season 2
- Main article: Owen Sleater Season 3
- Nucky Thompson: Employer, boss of the organization (deceased)
- Eli Thompson: Employer's brother, former Atlantic County Sheriff
- Lolly Steinman: Former employer, Casino manager
- Manny Horvitz: Associate (deceased)
- Mickey Doyle: Associate (deceased)
- Jimmy Darmody: Predecessor as Nucky's bodyguard (deceased)
- Tunney: Successor as Nucky's bodyguard (deceased)
- Arnold Rothstein: Bootlegging associate, employer's partner (deceased)
- Waxey Gordon: Bootlegging associate, employer's partner
- Chalky White: Bootlegging associate, employer's partner, African American community leader (deceased)
- Dunn Purnsley: African American labor leader, Chalky's lieutenant (deceased)
- Lucky Luciano: Bootlegging associate
- Meyer Lansky: Bootlegging associate
- Herman Kaufman: Bootlegging associate (deceased)
- Bill McCoy: Employer's liquor supplier
- Gyp Rosetti: Nucky's enemy and former customer (deceased)
- Tonino Sandrelli: Gyp's lieutenant (deceased)
- Victor Sickles: Tabor Heights Sheriff, bootlegging associate (deceased)
- John McGarrigle: Former employer (deceased)
- Del Grogan: Colleague in IRA, traitor (deceased)
- Bill Neilan: Colleague in IRA
- Patrick: Colleague in IRA
- Daniel Fitzgerald: Colleague in IRA
- Nucky Thompson: "What are your talents, Mr. Sleater?"
- "Making people stop."
- Nucky: "Stop what?"
- "Whatever it is you don't want them to be doing."
- "Leadin' me on a merry chase these five months. You traiterous fuck! (spits)" (Peg of Old)
- "These fuckers need to learn respect." (Resolution)
- "Bone for tuna" (Bone for Tuna)
- "There is word from Mr. Rothstein: Four fatalities- none of them Gyp Rosetti." ("You'd be Surprised")
- "It's just a business in the end... Ask the man buried in the coal mine. Or digging the canal; working the slaughterhouse. No one asks where what they want comes from they just want it. And believe what suits them." Margaret: And that's your peace with it. "There's no halfway. And there's- there's no excuse either- I'm in it now. And when I'm done I'll- I'll walk away." ("The Milkmaid's Lot")
|Season two appearances|
|21||Ourselves Alone||A Dangerous Maid||What Does the Bee Do?|
|Gimcrack & Bunkum||The Age of Reason||Peg of Old||Two Boats and a Lifeguard|
|Battle of the Century||Georgia Peaches||Under God's Power She Flourishes||To the Lost|
|Season three appearances|
|"Resolution"||"Spaghetti and Coffee"||"Bone for Tuna"||"Blue Bell Boy"|
|"You'd Be Surprised"||"Ging Gang Goolie"||"Sunday Best"||"The Pony"|
|"The Milkmaid's Lot"||"A Man, A Plan..."||"Two Imposters"||"Margate Sands"|