Question: What actor had varying roles in twenty episodes of CBS's "Gunsmoke" with the actor who was best known  for portraying Marshal Matt Dillon for 20 years?

Context articles: List of Waterloo Road characters (series 3)
Gunsmoke
Gregg Palmer
Dennis Weaver
Gunsmoke: To the Last Man
Matt Dillon (Gunsmoke)
James Arness
Paul Fix
Arvo Ojala
The Saint of Fort Washington

The following is a list of characters who first appear in the third series of the BBC school drama "Waterloo Road", in order of first appearance.
 The third series consists of twenty episodes, first broadcast from 11 October 2007 to 13 March 2008.
 The first episode adds deputy head Eddie Lawson, English teacher Jasmine Koreshi and head of music and drama Matt Wilding and pre-existing supporting characters Grantly Budgen and Davina Shackleton to the main cast, alongside pupil characters Karla Bentham, Bolton Smilie, Aleesha Dillon and Danielle Harker, canteen assistant and Bolton's mother Candice Smilie and school secretary Bridget Morley.
 Pupil Paul Langley makes his first appearance in episode two.
 Incoming head teacher Rachel Mason completes the main cast upon her debut in the seventh episode, local developer Stuart Hordley appears from episode ten for the remainder of the series and pupil Michaela White appears for the first time in episode twelve.
Gunsmoke is an American radio and television Western drama series created by director Norman Macdonnell and writer John Meston.
 The stories take place in and around Dodge City, Kansas, during the settlement of the American West.
 The central character is lawman Marshal Matt Dillon, played by William Conrad on radio and James Arness on television.
 When aired in the UK, the television series was initially titled Gun Law, later reverting to "Gunsmoke".
Gregg Palmer (born Palmer Edvind Lee; January 25, 1927 – October 31, 2015) was an American actor, known primarily for his work in television westerns.
 He appeared from 1960-1975 in varying roles in twenty episodes of CBS's "Gunsmoke" with James Arness, thirteen segments of the syndicated "Death Valley Days", and nine episodes of NBC's "The Virginian" starring James Drury in the title role.
 He guest starred five times on "Bonanza", NBC's longest-running western.
William Dennis Weaver (June 4, 1924 – February 24, 2006) was an American actor who was best known for his work in television and films.
 Weaver's two most notable roles were as Marshal Matt Dillon's trusty helper Chester Goode on the CBS western "Gunsmoke" and as Deputy Marshal Sam McCloud on the NBC police drama "McCloud".
 He appeared in the 1971 television film "Duel", the first film of director Steven Spielberg.
 He is also remembered for his role as the twitchy motel attendant in Orson Welles's film "Touch of Evil" (1958).
Gunsmoke: To the Last Man is a 1992 American TV-movie starring James Arness as retired Marshal Matt Dillon and featuring Pat Hingle.
 Hapless rustlers make the fatal mistake of stealing Matt Dillon's cattle and Dillon blunders into the gory Pleasant Valley War during the process of hunting them down and killing two of them.
 The film, set in the 1880s, was directed by Jerry Jameson and based upon the long-running American television series "Gunsmoke" (1955 to 1975).
 The supporting cast features Matt Mulhern as Will McCall, Joseph Bottoms as villainous Tommy Graham, and Morgan Woodward as Sheriff Abel Rose.
Matt Dillon is a fictional character featured on both the radio and television versions of "Gunsmoke".
 He serves as the U.S. Marshal of Dodge City, Kansas, who works to preserve law and order in the western frontier of the 1870s.
 The character was created by writer John Meston, who envisioned him as a man "...whose hair is probably red, if he's got any left.
 He'd be handsomer than he is if he had better manners but life and his enemies have left him looking a little beat up, and I suppose having seen his mother (back about 1840) trying to take a bath in a wooden washtub without fully undressing left his soul a little warped.
 Anyway, there'd have to be something wrong with him or he wouldn't have hired on as a United States Marshal in the heyday of Dodge City, Kansas."
 Notwithstanding Meston's original vision, the character evolved considerably during "Gunsmoke"' s nine-year run on CBS Radio and its 20-year run on CBS Television.
James Arness (May 26, 1923 – June 3, 2011) was an American actor, best known for portraying Marshal Matt Dillon for 20 years in the television series "Gunsmoke".
 Arness has the distinction of having played the role of Dillon in five separate decades: 1955 to 1975 in the weekly series, then in "" (1987) and four more made-for-television "Gunsmoke" films in the 1990s.
 In Europe, Arness reached cult status for his role as Zeb Macahan in the western series "How the West Was Won".
 He was the older brother of actor Peter Graves (1926–2010).
Peter Paul Fix (March 13, 1901 – October 14, 1983) was an American film and television character actor, best known for his work in Westerns.
 Fix appeared in more than a hundred movies and dozens of television shows over a 56-year career spanning from 1925 to 1981.
 Fix was best known for portraying Marshal Micah Torrance, opposite Chuck Connors's character in "The Rifleman" from 1958–1963.
 Fix later appeared with Chuck Connors in the 1966 western film "Ride Beyond Vengeance".
Arvo Ojala (February 21, 1920 in Seattle, Washington – July 1, 2005 in Gresham, Oregon) was a Hollywood technical advisor on the subject of quick-draw with a revolver.
 He also worked as an actor; his most famous role was that of the unnamed man shot by Marshal Matt Dillon in the opening sequences of the long-running television series "Gunsmoke".
 As a joke on the producers, James Arness and Arvo actually did the opener once with Dillon falling to the ground.
The Saint of Fort Washington is a 1993 American drama film directed by Tim Hunter and starring Matt Dillon and Danny Glover.
 Dillon won best actor at the 1993 Stockholm Film Festival for his performance.