The thing about 'The Rifleman' is the abundance of future stars who were unknowns on this show.
The Roku Channel (free) has all five seasons of The Rifleman, and it's absolutely amazing how many stars were on it. From a young, straight-eyed Jack Elam (he's in 5 over the years, and the eye starts misaligning as the seasons go on) to Adam West. Dennis Hopper is in two S1 episodes, Ida Lupino directs an episode (S3 E26 'Assault') Richard Anderson is great in 4 or 5 , Claude Akins (3) (who I didn't know was half Indian), Warren Oates (5), Agnes Morehead (Endora, on 'Bewitched'), Lee Van Cleef (4) - Oates and Van Cleef are both is S2 E31 'The Prodigal' - Robert Culp is in two of them, the first as a very unconvincing teenager in S2 E19 'Hero'. He seems older than Chuck Connors in his manner. The second appearance is fantastic, as a bounty hunter S4 E20 "Man From Salinas". He also wrote 'Waste' part 1 and 2, which began S5, starring Vito Scotti as a Mexican bandit with the worst teeth you've ever seen. Speaking of Mexican bandits, Martin Landau plays a great one in S4 E1 "The Vaqueros". William Schallert is in a couple, Cesare Danova, Vic Morrow, Buddy Hackett (2), Sammy Davis, Jr. (the highest rated episode on IMDB)(2), Michael Ansara (Barbara Eden's husband, and famously, Klingon commander Kang), Kevin McCarthy from 'Invasion of the Body Snatchers' plays a very good Mark Twain (opposite a pool shark Jack Elam), Robert Vaughn, Michael Landon and Dan Blocker, pre-Bonanza, a very young Richard Keil ('Jaws' from James Bond), James Coburn (2), Lon Chaney, Jr. I'm sure I'm missing some big ones. Richard Donnor directed a handful, as did B-movie noir director Joseph H. Lewis (51), Arthur Hiller, and Sam Peckinpah. Paul Mazursky wrote some episodes.
When you watch a bunch of them, you notice the same supporting actors in multiple episodes:
John Milford - 11
John Anderson (great!) - 11
Chris Alcaide - 10
Peter Whitney - 9 - different in each one
Dabbs Greer - 8
Mel Carter - 8
Richard Devon - 7 episodes, and he's great in each. My favorite guest star.
Royal Dano - 5, including as a neighbor who thinks he's Lincoln. Dano played Lincoln a lot, and Disney used his voice for the Hall of Presidents. Another stand-out is 'The Sheridan Story' S1 E16, as a war-wounded Confederate soldier holed up at the McCain ranch.
John Dehner - 4, and he's always fantastic, too.