Hägar the Horrible is the title and main character of an American comic strip created by cartoonist Dik Browne and syndicated by King Features Syndicate. It first appeared on February 4, 1973  (in Sunday papers) and the next day in daily newspapers, and was an immediate success. Following  Browne's retirement in 1988, his son Chris Browne (May 1952–February 5, 2023) continued the strip until his own death, with artwork by Gary Hallgren. As of 2010, Hägar is distributed to 1,900 newspapers in 56 countries and translated into 12 languages. The strip is a caricature commenting on modern-day life in the United States through a loose interpretation of Viking Age Scandinavian life.
 "Hagar the Terrible" was the nickname given to the late Dik Browne by his sons; Browne adapted the name to Hägar the Horrible for the purposes of alliteration. After his death, Dik Browne's sons changed the title of the strip to Dik Browne's Hägar the Horrible in tribute. The name is pronounced Hay-gar according to Chris Browne.
 Hägar (sometimes written "Hagar") is a shaggy, scruffy, overweight, red-bearded Viking. He regularly raids England and sometimes France. Animation-industry writer Terence J. Sacks notes the juxtaposition of contrary qualities that make Hägar endearing to the reader: "Hägar's horned helmet, rough beard and shaggy tunic make him look somewhat like a caveman or Opera-Viking, but you also know Hägar has a soft underbelly occasionally exposed."
 The strip is set in the Middle Ages in an unnamed coastal village somewhere in Norway. Hägar's Norwegian lineage was revealed at least once in a daily strip (July 18, 1984). Hamlet asks Hägar if he can tell people they're Norwegian. Hägar replies that it isn't necessary: "It might sound like bragging."
 Although anachronisms occur, they are not deliberate mainstays of the strip, as in other period burlesque strips like The Wizard of Id. The strip follows a standard gag-a-day daily format with an extended color sequence on Sundays.
 Much of the humor centers around Hägar's interactions with his longship crew, especially "Lucky Eddie" (when on voyages or during periodic sacking and looting raids). Sometimes the humor would be at the tavern with the other Vikings, or Hagar dealing with his family, who are not like stereotypical Vikings. Supporting characters include his overbearing, nagging and occasionally jealous wife, Helga; their brilliant and sensitive son, Hamlet; their pretty but domestically hopeless daughter, Honi; Helga's pet duck, Kvack; Hägar's loyal and clever dog, Snert, and other secondary, recurring characters.
 Hägar the Horrible uses a clear, sparse editorial-style line drawing, with minimal foreground or background detail, shading or embellishment. Observers argue this is likely derived from Dik Browne's experience as a courtroom illustrator and illustrator of maps of important World War II battles before 1942, plus his experience as an illustrator (Staff Sergeant) attached to a U.S. Army Engineer unit where he drew technical diagrams, maps, and other documents requiring very clear depictions. Before Hägar, Browne was best known for co-creating the comic strip Hi and Lois with his partner, Beetle Bailey creator Mort Walker. Browne was reportedly the real-life inspiration for the character Plato, the intellectual private in Beetle Bailey.
 Dik Browne based the characters on his family. His son Chris said, "And he was a big man like me. He was three hundred pounds and six feet two and had a flaming red beard."
 Other recurring minor characters include an unnamed psychic or soothsayer, whom Honi and Hägar regularly consult, a balding waiter at Helga's favorite restaurant, "The King of England", and various Anglo-Saxon raiders who serve as Hägar's friends and rivals, such as Dirty Dirk and Mean Max.
 An example of one strip highlighting Hägar's good intentions but cluelessness: Hägar returns from looting Paris with a present for his wife, Helga. He tells her it was ripped off a tub in a palace. He then turns on the faucet and eagerly encourages her to watch. When nothing happens, Hägar comments, "That's funny, when I turned it on in the palace, water came out."
 Hägar made his first animated appearance in a brief sketch paired with an interview with creator Dik Browne in the special The Fantastic Funnies broadcast on CBS May 15, 1980. 
Scott Beach (uncredited) provided the voice while the animation was produced by Bill Melendez and Lee Mendelson.
 A live-action Hägar sketch was included in the special Mother's Day Sunday Funnies broadcast May 8, 1983 on NBC.
 In 1989, an animated television special was aired, Hägar the Horrible: Hägar Knows Best produced by Hanna-Barbera and aired on CBS, based on the very first plotline when the strip began in 1973. Hägar returns home from battle after two years—and faces a major culture shock. His son Hamlet has bilged out of the Viking Academy, and his beloved daughter Honi is now dating a minstrel named Lute. Hägar blames Helga for allowing Honi to date Lute and being okay with Hamlet reading books. Hägar breaks up his daughter and trains his son in archery and other Viking venues. However, after seeing how unhappy his children have become, as well as other Vikings calling his kids weird, Hägar takes charge in his own way and sets things right.
The special starred Peter Cullen as Hägar, Lainie Kazan as Helga, Lydia Cornell as Honi, Josh Rodine as Hamlet, Jeff Doucette as Lucky Eddie, Don Most as Lute and Frank Welker as Snert, as well as providing additional voices.
It is available on DVD within the "Advantage Cartoon Mega Pack" set.
 Variety reported in 2003 that Abandon Pictures had acquired the film rights to the comic strip and planned a live-action theatrical feature based on the character. In late 2014, Chris Browne confirmed that a deal was made with Sony Pictures to produce a film based on the character.
 On November 10, 2020, it was announced a CGI animated series co-produced by King Features and The Jim Henson Company is currently in the works. The series will be animated by Henson Digital Puppetry Studio.
 Hägar the Horrible, a scrolling platform game, was released by Kingsoft for the Amiga in 1991. It was ported to Commodore 64 for the German market.
 All titles are mass-market paperbacks by Dik Browne, unless otherwise noted.
 Hägar the Horrible is featured in the Universal Studios Florida theme park Islands of Adventure, seen on a boat on top of Toon Extra in Toon Lagoon.