[[quoteright:280:https://static.tvtropes.org/pmwiki/pub/images/3x01ethanrom_55.jpg]]
[[caption-width-right:280:Be afraid.]]

William Reibert Mapother Jr. (born April 17, 1965) is an American actor and former teacher.

He is probably best known to audiences as [[TheMole Ethan Rom]] on ''Series/{{Lost}}'' or [[JerkAss Richard Strout]] in ''In The Bedroom''. He often ends up cast in the roles of villains or creeps, but he's a versatile actor with a pretty eclectic resume. Despite his reputation with general audiences as being utterly terrifying, he's actually a nice guy who also serves on the board of directors for the Screen Actor's Guild.

He is the first cousin of actor Thomas C. Mapother IV, better known as Creator/TomCruise. They have [[RealLifeRelative played together]] in some films.
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!!Film Roles
* 2000 Film/MissionImpossibleII as Wallis
* 2001 Film/{{Swordfish}} as Gabriel's Crew
* 2001 Film/VanillaSky (cameo, clubgoer)
* 2002 Film/InTheBedroom as Richard
* 2002 Film/MinorityReport as Hotel Clerk
* 2004 Film/TheGrudge as Matthew Williams
* 2005 Film/LordsOfDogtown as Donnie
* 2008 Film/TheBurrowers as Will Parcher
* 2008 Film/{{Hurt}} as Darryl Coltrane
* 2011 Film/AnotherEarth as John Burroughs
* 2011 Film/{{Warrior}} as David Milligan
* 2013 Film/{{Jobs}} as Calligraphy Professor

!!Television Roles
* 2002 Series/{{CSI}} as Douglas Sampson
* 2003 Series/LawAndOrderSpecialVictimsUnit as Luke Edmunds
* 2004 Series/{{CSI Miami}} as Pete Keller
* 2004 Series/{{NCIS}} as Kyle Grayson
* 2005 Series/TheInside as Ronald Ewing
* 2005 Series/{{Threshold}} as Gunneson
* 2005 Series/CrossingJordan as Henry Bishop
* 2008 Series/CriminalMinds as Ian Corbin
* 2004-2010 Series/{{Lost}} as Ethan Rom
* 2009 Series/PrisonBreak as FBI Agent Chris Franco
* 2010 Series/LawAndOrderCriminalIntent as John Silvestri
* 2010 Series/HumanTarget as Sam Fisher
* 2011-2014 Series/TheMentalist as Richard Haibach
* 2012 Series/{{Justified}} as Delroy Baker
* 2012 Series/AmericanHorrorStoryAsylum as Misogynist Driver
* 2012 Series/BurnNotice as Garret Hartley
* 2013 Series/MadMen as Randall Walsh
* 2013 Series/{{Castle|2009}} as Carl Matthews
* 2014 Series/{{Constantine}} as Jacob Shaw
* 2016 Series/Supergirl2015 as Rudy Jones/Parasite

!!Videogames
* 2010 Videogame/FalloutNewVegas as Colonel Hsu
* 2010 Videogame/HaloReach as Air Control / Dispatch
* 2012 Videogame/TheSecretWorld as Paul Gamelin
* 2012 VideoGame/HitmanAbsolution as Agent 47 (Mapother was replacing series staple David Bateson in the role but fan backlash led to Bateson being brought back in, though Mapother’s motion capture for 47’s face was retained.)
* 2013 Videogame/LightningReturnsFinalFantasyXIII as Additional Voices
* 2016 VideoGame/Hitman2016 as Dino Bosco.

!!Tropes
* SlasherSmile: Can't seem to help it, poor guy.
* WhatCouldHaveBeen: William was supposed to replace Creator/DavidBateson as Agent 47 in ''VideoGame/HitmanAbsolution''. Square Enix, in a rare showing of common sense, realised their mistake they made at recasting when shown secret recordings Bateson and IOI had made to convince them to change their minds, and they agreed with the fan backlash, resulting in Bateson returning at the last minute. Mapother later voiced Dino Bosco, a target in ''VideoGame/Hitman2016'' as a CastingGag to this situation, with two [=NPC's=] noting he's not right for the role, and want him replaced by another actor named Dave Bateson, and are protesting and boycotting the film until this happens.
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