A showrunner (or colloquially a helmer ) is the top-level executive producer of a television series production,     who outranks other creative personnel, including episode directors, in contrast to feature films, in which the director has creative control over the production, and the executive producer's role is limited to investing. 
In a January 1990 submission to the United States Congress House Committee on the Judiciary Subcommittee on Courts, Intellectual Property, and the Administration of Justice, Barney Rosenzweig (then Executive Vice President and Chairman, Television Division of Weintraub Entertainment Group) wrote: 
"In the early days of Hollywood, no one questioned what Producer David O. Selznick was to Gone With the Wind, or Pandro Berman to all those Fred Astaire and Ginger Rodgers [ sic] films, or Walt Disney to his early work, or Arthur Freed to the MGM musical. They were the producers... the storytellers. Today in television, the producer is still that person: the show-runner. Television is a producer's medium. Ask the people who make and stand behind their shows – from Aaron Spelling to Stephen Cannell, Stephen Bocho [ sic], Len Hill, Edgar Scherick or Phil de Guerre [Philip DeGuere Jr.]. The definition of who does what in television today is not that different from what it was generally in Hollywood before a few critics in France coined the term ' auteur' and the Writer's Guild took the producers, their traditional nemesis, to court – thus all but destroying the Producer's Guild and giving leave for the studios themselves to usurp the name producer." 
Traditionally, the executive producer of a television program was the chief executive, responsible for the show's creative direction and production. Over time, the title of executive producer was applied to a wider range of roles—from a senior writer, to someone who arranges financing, to an "angel" who holds the title as an honorific with no management duties in return for providing backing capital. The term showrunner was created to identify the executive producer who holds ultimate management and creative authority for the program. The blog and book Crafty Screenwriting defines a showrunner as "the person responsible for all creative aspects of the show and responsible only to the network (and production company, if it's not [their] production company). The boss. Usually a writer." 
Los Angeles Times columnist Scott Collins describes showrunners as: 
"Hyphenates", a curious hybrid of starry-eyed artists and tough-as-nails operational managers. They're not just writers; they're not just producers. They hire and fire writers and crew members, develop story lines, write scripts, cast actors, mind budgets and run interference with studio and network bosses. It's one of the most unusual and demanding, right-brain/left-brain job descriptions in the entertainment world....[S]howrunners make – and often create – the show and now more than ever, shows are the only things that matter. In the " long tail" entertainment economy, viewers don't watch networks. They don't even care about networks. They watch shows. And they don't care how they get them.
Shane Brennan, the showrunner for NCIS and NCIS: Los Angeles, stated in an interview that:
... the moniker was created to identify the producer who actually held ultimate management and creative authority for the program, given the way the honorific "executive producer" was applied to a wider range of roles. There's also the fact that anyone with any power wanted a producer's credit, including the leading actors, who often did no more than say the writers' lines. "It had got to the stage where it was incredibly confusing; there were so many production credits no one knew who was responsible." 
The Writers Guild of Canada, the union representing screenwriters in Canada, established the Showrunner Award in 2007, at the annual Canadian Screenwriting Awards. The first Showrunner Award was presented in April 2007 to Brad Wright, executive producer of Stargate Atlantis and Stargate SG-1. 
In the first decade of the 21st century, the concept of a showrunner, specifically interpreted as a writer or presenter with overall responsibility for a television production, began to spread to the British television industry.  "Nonetheless, the show runner production model is still less common in drama production in the UK" than it is in the U.S., scholars Ruth McElroy and Caitriona Noonan wrote in 2019. 
The first British comedy series to use the term was My Family (2000–11), which had several showrunners in succession. Initially, the show was overseen by creator Fred Barron from series 1–4. Ian Brown and James Hendrie took over for series 5, followed by American writer Tom Leopold for series 6. Former Cheers showrunner Tom Anderson was in charge from series 7 to the final series, series 11. 
The first writer appointed the role of showrunner on a British primetime drama was Tony McHale, writer and creator of Holby City, in 2005.  Jed Mercurio had carried out a similar role on the less conspicuous medical drama Bodies (2004–2006).  But Russell T Davies' work on the 2005 revival of Doctor Who brought the term to prominence in British television (to the extent that in 2009 a writer for The Guardian wrote that "Over here, the concept of 'showrunner' has only made it as far as Doctor Who"). 
In an interview, Davies said that he felt the role of the showrunner was to establish and maintain a consistent tone in a drama.  Doctor Who remains the most prominent example of a British television programme with a showrunner, with Steven Moffat having taken over the post from Davies from 2010 until 2017.   Chris Chibnall later took over from Moffat.  Davies returned, following Chibnall's departure. The term has also been used to refer to other writer-producers, such as Tony Jordan on Moving Wallpaper and Echo Beach, Ann McManus on Waterloo Road, Adrian Hodges on Primeval  and Jed Mercurio on Bodies,  Line of Duty,  and Critical. 
para. 2: "He or she is… always an executive producer."