Under the alias of Don Sturdy, Hesseman made his first television appearances, including the episode "Public Affairs: DR-07" of the show
Dragnet in 1968. He portrayed a hippie named Jesse Chaplin, the editor of an underground newspaper. In this
Dragnet episode, his character was a panelist on a TV show opposite Sgt. Friday and Officer Gannon. He played a
bit part in two final-season episodes of
The Andy Griffith Show. In the episode "Sam for Town Council", Hesseman played a character named Harry, who has an exchange with Emmett Clark (
Paul Hartman), who is running for town council against
Sam Jones, played by
Ken Berry. Harry complains to Emmett how poor the fishing has been at a nearby fishing spot. Emmett promises to stock the pond with big
perch in exchange for Harry's vote. Harry agrees and wears a campaign button supporting Emmett in the race. In the episode "Goober Goes to an Auto Show", Hesseman, also credited as Don Sturdy, played the counter boy, serving hot dogs and root beers to Goober and his old trade-school rival Roy Swanson, played by
Noam Pitlik. On July 18, 1969, he appeared with the improvisational comedy group The Committee in several sketches on
The Dick Cavett Show, including one with guest
Janis Joplin. Hesseman also appeared in a number of skits as part of The Committee in the 1971 classic film
Billy Jack. Hesseman made several appearances as Mr. Plager, a member of the group therapy ensemble on
The Bob Newhart Show; Mr. Plager eventually came out as
gay. Hesseman became a playwright in the sixth season of the show, writing a play about the characters in the group. In several other episodes of
The Bob Newhart Show, Hesseman's voice can be heard as a TV announcer. at
Walt Disney World's
Disney's Hollywood Studios theme park Hesseman is best known for his role as DJ John "Dr. Johnny Fever" Caravella on the television sitcom
WKRP in Cincinnati from 1978 to 1982, a role Hesseman prepared for by working as a DJ in San Francisco at
KMPX-FM for several months. He was nominated for a
Primetime Emmy Award for Outstanding Supporting Actor in a Comedy Series in 1980 and 1981 for his portrayal of Fever. He reprised the role in nine episodes of
The New WKRP in Cincinnati, and also directed several episodes of that 1991-93 series revival. Hesseman portrayed Sam Royer, the man who married Ann Romano (
Bonnie Franklin) on the sitcom
One Day at a Time from 1982 to 1984. He then played history teacher Charlie Moore on the ABC series
Head of the Class for four seasons from 1986 to 1990. His film appearances included the comedy film
Police Academy 2: Their First Assignment (1985) as Captain Pete Lassard, the mystery film
Clue (1985) as the Chief of Police, and the Disney film
Flight of the Navigator (1986) as NASA research facility scientist Dr. Louis Faraday. Hesseman made three appearances on
Saturday Night Live, one in which he paid tribute to, and told jokes about, the recently deceased
John Belushi and the other in which NBC showed a picture of U.S. President
Ronald Reagan, which Hesseman
mooned off-camera. He also encouraged the viewing audience to moon the picture and send pictures in to NBC. In 1994, he introduced lost footage of Janis Joplin in a documentary on
Woodstock. In 1995, Hesseman played the role of the
Marquis de Sade in
Quills at the
Geffen Playhouse in
Westwood, California, which included one scene in which he was fully naked. In 2001, Hesseman had a role on three episodes of ''
That '70s Show''. In 2002, he played Larry Hertzel in
Alexander Payne's comedy-drama
About Schmidt. In 2006, Hesseman played the unorthodox Judge Robert Thompson in three episodes of
Boston Legal, and also appeared in an episode of
House. During his appearance as Judge Thompson, Hesseman paid
homage to his role as a teacher in his earlier ABC series by hearing a court case while sitting atop the judge's bench, just as the character of Mr. Moore taught his class atop his desk. In 2007, he played The Chemist on
HBO's
John From Cincinnati. He guest-starred as an announcer at a horse track on
Psych, in the episode "And Down the Stretch Comes Murder.” Hesseman guest-starred on the 2007 season premiere of NBC's
ER, playing a man tripping on
magic mushrooms who may or may not have been an
orthopedist from another hospital. In 2009, he appeared in
Rob Zombie's
Halloween II and the
Sandra Bullock film,
All About Steve. Hesseman starred in
The Sunshine Boys at the New Theatre Restaurant in
Overland Park, Kansas, from September to November 2010. In February 2011, he portrayed Dr. Elliot D. Aden in the 11th-season
CSI: Crime Scene Investigation episode "Turn On, Tune In, Drop Dead.” Dr. Aden was head of Department of Defense project called Stonewall at WLVU, which did research in fringe psychological concepts such as
extrasensory perception and
out-of-body experiences. ==Personal life and death==