Here is his whole filmography, thanks to
TV Tome:
Starring Roles
8 Simple Rules for Dating My Teenage Daughter (2002) - Paul Hennessy
Clifford the Big Red Dog (2000) - Clifford
Hearts Afire (1992) - John Hartman
Fish Police (1992) - Inspector Gil
Hooperman (1987) - Harry Hooperman
Three's a Crowd (1984) - Jack Tripper
Get Rich Quick (1977) - Panelist
Three's Company (1977) - Jack Tripper
The Waltons (1972) - Rev. Fordwick
Guest Starring Roles
All Access - Himself (From the TV Land Awards) - All Access: TV Land Awards (2004)
The Hollywood Squares (1998) - Himself - 9/29/03 - 10/3/03 (2003)
The Wayne Brady Show (syndicated) - Guest - 9/1/03 (2003)
King of the Hill - - Witches of East Arlen (2003)
The Wayne Brady Show (syndicated) - Guest - 5/6/03 (2003)
The View - Himself - February 18, 2003 (2003)
The Late Late Show with Craig Kilborn - Himself - Monday, February 17, 2003 (2003)
The Hollywood Squares (1998) - Himself - 2/10/2003 - 2/14/2003 (2003)
The Hollywood Squares (1998) - Himself - 1/20/2003 - 1/24/2003 (2003)
Scrubs - Mr. Dorian (Flashback scene) - My Lucky Day (2002)
Biography - Himself - John Ritter: In Good Company (2002)
Live with Regis and Kathie Lee - Himself - Primetime Special September 17, 2002 (2002)
The View - Himself - September 16, 2002 (2002)
The Wayne Brady Show (syndicated) - Guest - 9/2/02 (2002)
Live with Regis and Kathie Lee - Himself - July 15, 2002 (2002)
TVography - Himself - Suzanne Somers: Mastering Success (2002)
Scrubs - Mr. Dorian - My Old Man (2002)
Wednesday 9:30 (8:30 Central) - Himself - The Art of Groveling (2002)
Felicity - Andrew Covington - Kiss and Tell (2002)
E! True Hollywood Story - Himself (Archived) - Suzanne Somers (2002)
The Tonight Show with Jay Leno - Guest (cameo) - Show #2219 (2002)
Law & Order: Special Victims Unit - Dr. Richard Manning - Monogamy (2002)
The Tonight Show with Jay Leno - Guest (cameo) - Show #2191 (2002)
Felicity - Andrew Covington - A Perfect Match (2001)
Felicity - Andrew Covington - The Storm (2001)
Felicity - Andrew Covington - Oops...Noel Did It Again (2001)
Tucker - Marty - Homewrecker for the Holidays (2001)
T.V. Funhouse - Himself - Chinese New Years Day (2001)
Live with Regis and Kathie Lee - Himself - December 18, 2000 (2000)
Felicity - Andrew Covington - Kissing Mr. Covington (2000)
Felicity - Andrew Covington - Hello, I Must Be Going (2000)
Felicity - Andrew Covington - The Anti-Natalie Intervention (2000)
Family Law - Father Andrews - Possession is Nine Tenths of the Law (2000)
Batman Beyond - Dr. David Wheeler - The Last Resort (2000)
Chicago Hope - Joe - Simon Sez (2000)
E! True Hollywood Story - Himself - Dorothy Stratten (2000)
Intimate Portrait - Himself - Joanna Kerns (2000)
Intimate Portrait - Narrator - Rue McClanahan (2000)
Touched by an Angel - Sheriff Tom McKinsley - Black Like Monica (1999)
Veronica's Closet - Tim - Veronica's Favorite Year (1999)
E! True Hollywood Story - Himself - Three's Company (1998)
Ally McBeal - George Madison - Story of Love (1998)
Ally McBeal - George Madison - It's My Party (1998)
Buffy the Vampire Slayer - Ted - Ted (1997)
King of the Hill - Eugene Grandy - The Son That Got Away (1997)
Over the Top - Justin Talbot - The Nemesis (1997)
Ordinary/Extraordinary - Host - Pilot (1997)
Dead Man's Gun - Mcdonacle - The Great Mcdonacle (1997)
Touched by an Angel - Mike O'Connor - Random Acts (1996)
Wings - Stuart Davenport - Love Overboard (1996)
NewsRadio - Dr. Frank Westford - The Shrink (1995)
Dave's World - Himself - The Accidental Tourists (1995)
Dave's World - Himself - A Room With a View (1994)
The Larry Sanders Show - Himself - The Fourteenth Floor (1994)
The Larry Sanders Show - Himself - Off Camera (1993)
Disneyland - - Celebrate The Spirit: Disney's All Star 4th Of July Spectacular (1992)
Anything but Love - Patrick Serreau - Stop Me Before I... Again (2) (1991)
Anything but Love - Patrick Serreau - Stop Me Before I... Again (1) (1991)
Anything but Love - Patrick Serreau - Hello... Mali (3) (1991)
Anything but Love - Patrick Serreau - Martus Interruptus (2) (1991)
Anything but Love - Patrick Serreau - Say it Again, Han (1) (1991)
The Cosby Show - Ray Evans - Total Control (1991)
Problem Child - Ben - Problem Child (1990)
The Tonight Show Starring Johnny Carson - Guest - 890206 (1989)
Disneyland - Dudley Goode - Mickey's 60th Birthday (1988)
Life with Lucy - Himself - Lucy Makes a Hit with John Ritter (1986)
The Tonight Show Starring Johnny Carson - Guest - 850507 (1985)
The Tonight Show Starring Johnny Carson - Guest - 840302 (1984)
The Love Boat - - Japan Cruise: When Worlds Collide/The Captain and the Geisha/The Lottery Winners/The Emperor's Fortune (1) (1983)
The Love Boat - - Japan Cruise: When Worlds Collide/The Captain and the Geisha/The Lottery Winners/The Emperor's Fortune (2) (1983)
The Tonight Show Starring Johnny Carson - Guest - 820127 (1982)
The Tonight Show Starring Johnny Carson - Guest - 810821 (1981)
The Waltons - Reverand Matthew Fordwick (Flashbacks) - A Decade of the Waltons (1980)
The Associates (1979) - Chick [Me] - The Censors (1980)
The Tonight Show Starring Johnny Carson - Guest - 800225 (1980)
The Ropers - Jack Tripper - The Party (a.k.a.) Stanley, the Ladies Man (1979)
The Tonight Show Starring Johnny Carson - Guest - 781016 (1978)
The Love Boat - Dale Riley - Oh, Dale!/The Main Event/A Tasteful Affair (1977)
The Tonight Show Starring Johnny Carson - Guest - 770829 (1977)
The Tonight Show Starring Johnny Carson - Guest - 770506 (1977)
Hawaii Five-O - Mike Welles - Dealer's Choice -- Blackmail (1977)
Phyllis - - The New Job (1976)
Rhoda - Jerry Blocker - Attack on Mr. Right (1976)
Starsky and Hutch - Tom Cole - The Hostages (1976)
The Rookies - Hap Dawson - Reluctant Hero (1975)
The Mary Tyler Moore Show - Rev. Chatfield - Ted's Wedding (1975)
The Streets of San Francisco - John 'Johnny' Steiner - Murder by Proxy (1975)
Barnaby Jones - Joe Rockwell - The Price of Terror (1975)
Petrocelli - - Chain of Command (1975)
Mannix - Cliff - Hardball (1975)
Rhoda - Vince Mazuma - Chest Pains (1975)
The Bob Newhart Show - Dave - Sorry, Wrong Mother (1974)
Kojak - Kenny Soames - Deliver Us Some Evil (1974)
M*A*S*H - Pt. Carter - Deal Me Out (1973)
Medical Center - Unknown - End of the Line (1973)
The Waltons - Reverand Matthew Fordwick - The Sinner (1972)
Hawaii Five-O - Ryan Moore - Two Doves And Mr. Heron (1971)
Dan August - - Quadrangle for Death (1970)
Breaking News - Lloyd Fuchs - Pilot (0)
The Ellen Show - Percy Moss - Gathering Moss (aka The Flood aka For God's Sake) (0)
Celebrity Profile - Himself - Jamie Lee Curtis
Dan August - campus revolutionary
Family Feud - Himself
Headliners and Legends - Himself - Don Knotts
Headliners and Legends - Himself - Calista Flockhart
Jimmy Kimmel Live - Himself - April 21, 2003
Late Night with Conan O'Brien - Himself
Live with Regis and Kathie Lee - Co-Host/Himself - April 16, 2001
Live with Regis and Kathie Lee - Himself - November 1998
Movin' On - Casey - Landslide
Nature - Narrator - Dogs: The Early Years
Owen Marshall, Counselor At Law - Greg
Phyllis - Crooked City Supervisor
Pryor's Place - - The Show Off
Rank - Himself (Archived) - Sitcoms We Secretly Love
The Dating Game - Himself - 1967
The Hollywood Squares (1998) - Himself
The Wayne Brady Show (syndicated) - Himsef - 05/06/03
Movie/Mini-Series/Special Roles
Clifford The Big Red Dog: The Movie (2004) - Clifford
Bad Santa (2003) - Mall Manager
A Life of Laughter: Remembering John Ritter (2003) - Himself
Given a Chance ... A Little Girl's Journey (2003) - Himself
Manhood (2003) - Eli
Man Of The Year (2002) - Bill
Tadpole (2002) - Stanley Grubman
Lost in the Pershing Point Hotel (2000) - Christian Therapist (cameo)
Panic (2000) - Dr. Josh
Terror Tract (2000) - Bob Carter (Segment "Make Me an Offer")
Tripfall (2000) - Tom Williams
Holy Joe (1999) - Joe Cass
It Came From the Sky (1999) - Donald Bridges
Lethal Vows (1999) - Dr. David Farris
Bride of Chucky (1998) - Chief Warren Kincaid
Chance of a Lifetime (1998) - Tom Maguire
Dead Husbands (1998) - Dr. Carter Elston
I Woke Up Early The Day I Died (1998) - Robert Forrest
Montanta (1998) - Dr. Wexler
Shadow of Doubt (1998) - Steven Mayer
A Child's Wish (1997) - Ed Chandler
A Gun, a Car, a Blonde (1997) - Duncan
Loss of Faith (1997) - Bruce Simon Barker
Nowhere (1997) - Moses Helper (cameo)
Sink or Swim (1997) - Hank
The Colony (1996) - Rick Knowlton
Mercenary (HBO-TV) (1996) - Jonas Ambler
Sling Blade (1996) - Vaughan Cunningham
Unforgivable (1996) - Paul Hegstrom
The Barefoot Executive (1995) - Roger
Gramps (1995) - Clarke MacGruder
North (1994) - Ward Nelson
The Only Way Out (1993) - Jeremy Carlisle
Noises Off... (1992) - Garry Lejeune/Roger Tramplemain
Stay Tuned (1992) - Roy Knable
Problem Child 2 (1991) - Ben Healy
The Summer My Father Grew Up (1991) - Paul
The Dreamer of Oz (1990) - Lyman Frank Baum
It (1990) - Ben
Problem Child (1990) - Ben Healy
Stephen King's It (1990) - Ben Hanscom
My Brother's Wife (1989) - Barney
Skin Deep (1989) - Zach
Tricks of the Trade (1988) - Donald Todsen (Cameo)
The Last Fling (1987) - Phillip Reed
Prison for Children (1987) - David Royce
Real Men (1987) - Bob Wilson
The Flight of Dragons (1986) - Peter Richardenson
A Smoky Mountain Christmas (1986) - Judge Harold Benton
Unnatural causes (1986) - Frank Coleman
Letting Go (1985) - Alex
Love Thy Neighbor (1984) - Danny Loeb
Sunset Limousine (1983) - Alan O'Black
In Love with an Older Woman (1982) -
Pray TV (1982) - Tom McPherson
They All Laughed (1981) - Charles Rutledge
Wholly Moses (1980) - Satan (The Devil)
Wholly Moses (1980) - Satan (The Devil)
The Comeback Kid (1980) - Bubba Newman
Heartbeat (1980) - Bill Grant
Hero at Large (1980) - Steve Nichols
Americathon (1979) - President Chet Roosevelt
The United Cerebral Palsy Weekend With The Stars Telethons (1997) - Co-Host
Breakfast in Bed (1978) - Paul
Leave Yesterday Behind (1978) - Paul Stallings
Ringo (1978) -
Nickelodeon (1976) - Franklin Frank
The Night That Panicked America (1975) - Walter Wingate
The Stone Killer (1973) - Officer Mort
The Other (1972) - Rider
Evil Roy Slade (1971) - Minister
Scandalous John (1971) - Wandell
Echoes of the Sixties - Himself
When Cowboys Were King (2003) History Channel Documentary - Himself