The American comedy actor Fred Willard, who has died aged 86, never took top billing on screen, but he found his niche as a scene-stealer in the mockumentaries of Christopher Guest, among others, usually playing characters invested with authority who prove to be inept, clueless or simply unintentionally funny.

In his first, This is Spinal Tap (1984), a satire of reverential rock documentaries, directed by Rob Reiner and starring Guest, Willard is an upbeat lieutenant organising a gig for a fictional British heavy-metal band in a US airforce base hangar – after they have to cancel dates at bigger venues because of low ticket sales.

In his squirming welcome to the band for the base’s “monthly at-ease weekend”, he announces a 7pm start and jokes about their long hair. “These haircuts wouldn’t pass military muster, believe me,” he says, jovially, “although I shouldn’t talk – my hair’s getting a little shaggy, too. Better not get too close to you. They’ll think I’m part of the band!”

As the gig gets under way, with the audience sitting at tables and holding their hands over their ears while they try to chat, it becomes clear that the venue is totally unsuitable. One of the band smashes his guitar and storms off the stage.

Willard’s talent for improvised dialogue made him perfect for his role and he was able to draw on two years’ experience in the army. “I knew the military sensibility,” he recalled. “The guy’s trying to fit in. He was the entertainment director – he wanted to seem like a regular guy.”

After his debut, Willard became an informal member of the repertory company of actors that Guest directed in a string of subsequent films. In Waiting for Guffman (1996), Willard played a travel agent who stars with his wife (Catherine O’Hara) alongside other Missouri residents in an amateur stage production. While doing for small-town acting troupes what This is Spinal Tap did for rock bands, the film retains an affection for those it satirises.

Best in Show (2000) was more blunt, homing in on bizarre dog owners and their neurotic pets taking part in a kennel club competition, with Willard as the TV commentator. “To think that in some countries these dogs are eaten,” he remarks, deadpan. His inappropriate comments also include musing about whether bribes would sway the judges and pointing out a dog trying to hump the leg of its owner.

Music was back in the spotlight for A Mighty Wind (2003), about three acts from the 1960s folk revival staging a memorial concert decades later for their much-loved promoter. In his best buffoon mode, Willard plays the failed comedian-turned-road manager of the New Main Street Singers who laughs at his own jokes as he tries to get himself into the spotlight with a stream of lame punchlines and the catchphrase “Wha’ Happened?”.

For Your Consideration (2006) had Hollywood itself in Guest’s sights and was less mockumentary in its straight parody of unknown actors experiencing the Oscar buzz after making a low-budget period drama. Willard steals the show once more as the TV entertainment news show host visiting the set and providing laughs with his vacuous questions and “fauxhawk” hairstyle.

Mascots (2016), Willard’s last film with Guest, premiered on Netflix, with humans – not dogs this time – fighting to win a contest. The director’s inspiration proved to be flagging, but Willard gave the picture one of its funniest scenes as a mascot coach interrogating Brad Williams, a dwarf actor, with dubious questions about how he manages to fit into his worm outfit.

Other directors utilised Willard’s comedy skills, most effectively Adam McKay in Anchorman: The Legend of Ron Burgundy (2004), with Willard cast as the director of a San Diego television news channel alongside Will Ferrell. In one scene, he tells a journalist that his schoolboy son “was on something called acid and was firing a bow and arrow into a crowd”, adding: “You know how kids are!”

Willard also made cameo appearances in endless television sitcoms, had a run of eight episodes in Roseanne (1995-97) as Scott, the star’s houseguest rekindling an old relationship, and was nominated for Emmy awards for his performances as fathers in Everybody Loves Raymond (Hank MacDougall, 2003-05) and Modern Family (Frank Dunphy, 2009-20).

Born in Shaker Heights, Ohio, to Ruth (nee Weinman) and Frederick Willard, a bank employee, Fred attended the Kentucky Military Institute and the Virginia Military Institute before army service in Germany.

After his two-year draft, he headed to New York. On a drama course there he teamed up with Gus Mocerino, who changed his name to Vic Grecco, and together they wrote sketches and formed the comedy duo Willard & Grecco, appearing in clubs and on TV entertainment shows until they split up in 1968.

While continuing with stand-up comedy, Willard started to get small acting roles on screen. His breakthrough came with Fernwood Tonight (1977), a satire on talk shows, when he played Jerry Hubbard, sidekick to Martin Mull’s smarmy host, Barth Gimble, giving a taste of what was to come.

However, he had to wait another seven years before his role in Spinal Tap and the subsequent Guest comedies made him one of the most loved American comedy actors and a regular on late-night chat shows. He was reunited with Guest when he played Mike Morton, Ed Begley Jr’s crude neighbour, in the 2013 sitcom Family Tree.

In 1968, Willard married Mary Lovell, a playwright; she died in 2018. He is survived by their daughter, Hope.

• Frederick Charles Willard, actor, born 18 September 1933; died 15 May 2020