Question: Walter O'Brien was played by which English actor?

Context articles: Kevin O'Brien (cricketer)
Elyes Gabel
Dub Taylor
Walter O'Brien (character)
Mick Walter
Kieran O'Brien
Mark Dymond
The Over-the-Hill Gang Rides Again
Richard O'Brien (disambiguation)
Eileen O'Brien (actress)

Kevin Joseph O'Brien (born 4 March 1984) is an Irish cricketer who plays for Railway Union Cricket Club and has played for several English county cricket clubs.
 He holds the world record for the fastest century ever scored at a World Cup, coming from 50 balls against England on 2 March 2011.
 An all-rounder, O'Brien is an aggressive right-handed middle to lower order batsman and a right-arm medium-fast bowler.
 He made his One Day International (ODI) debut in 2006 in Ireland's inaugural match.
 O'Brien played for Nottinghamshire in 2009, and in 2010 was awarded a contract with Cricket Ireland, making him one of six players with a full-time contract with the board.
 He has been Ireland's vice-captain since January 2012.
Elyes Cherif Gabel (born 8 May 1983) is an English actor.
 Among his most notable roles, he has portrayed Dr. Gupreet "Guppy" Sandhu in the "BBC" medical drama "Casualty", Dothraki Rakharo in Seasons 1 and 2 of the "HBO" series "Game of Thrones", and P.E. teacher Rob Cleaver in the BBC drama "Waterloo Road".
 He appeared in the "ITV" drama "Identity" and portrayed Detective Adam Lucas in Season 3 of "Body of Proof".
 He is currently starring in the CBS series "Scorpion" as computer genius Walter O'Brien.
Walter Clarence Taylor Jr. (February 26, 1907 – October 3, 1994), known as Dub Taylor, was an American character actor who from the 1940s into the 1990s worked extensively in films and on television, often in Westerns but in comedies.
 He was the father of actor Buck Taylor, who played the character Newly O'Brien on "Gunsmoke".
Walter O'Brien is the fictional lead character in the American drama television series, "Scorpion".
 The character is inspired by the real life of Walter O'Brien, a computer expert and hacker who at an early age hacked into NASA servers to obtain secure files and scored a 197 on a childhood IQ test.
 The character, played by actor Elyes Gabel, follows a loose trajectory of Walter O'Brien's real-life exploits that thwart terrorism and disasters in each episode of the series.
Mick Walter (born Michael E. Walter in Huddersfield, Yorkshire, in 1955), often referred to by the stage name Big Mick, is an English actor.
 He is known for appearing in television comedies, first appearing as Jack Large in "Blackadder".
 He has also appeared in "Black Books", "Green Wing" and "Psychoville".
Kieran O'Brien (born 1973 in Oldham, Lancashire) is an English actor.
Mark Dymond (born 1974, Wimbledon, London) is an English actor of Irish descent.
 In addition to appearances in films, he is known as Dr. Lorcan O'Brien, a major character in the 2007–2009 seasons of the TV drama series "The Clinic", among other TV shows.
 He married actress Jo Bourne-Taylor in 2004.
The Over-the-Hill Gang Rides Again starring Walter Brennan and Fred Astaire is a 1970 "ABC Movie of the Week" sequel to the Western comedy "The Over-the-Hill Gang".
 The supporting cast includes Edgar Buchanan, Andy Devine, Chill Wills, Lana Wood, and Burt Mustin (all of whom, except Wood, were in "The Over-the-Hill Gang").
 Like the 1969 original, the sequel involves aging Texas Rangers and was written by Richard Carr and directed by George McCowan.
 Pat O'Brien had played the second lead in the first film but his character was left out of the sequel and he was effectively replaced by Astaire, who was not in the original film.
 Richard Widmark played O'Brien's character in a quasi-remake two decades later entitled "Once Upon a Texas Train", in which the Over-the-Hill Gang, with an entirely new cast including Stuart Whitman, played supporting roles to Willie Nelson's train robber.
Richard O'Brien (born 1942) is an English actor, television presenter, writer and theatre performer.
Eileen O'Brien is an English actress who has played a wide variety of roles in British television over many years.
 She appeared in ITV soap opera, "Emmerdale" as Beattie Dixon, grandmother of Alex Moss, who turned up at the beginning of 2013 to look for her grandson.
 O'Brien previously appeared in the show as teacher, Bridget Burgess in 2006-2007.
 Back in 1987-1988, O'Brien had a recurring role in the BBC soap opera, "EastEnders"; she played Edie Smith, the mother of Linda Davidson's character, Mary.