After working almost exclusively with CBS from the beginning, Desilu frontman Desi Arnaz sold his first series to ABC in 1959, and that was only because CBS turned down what would become a classic crime drama.
The Untouchables began as a 2-part episode under that same name on the Westinghouse Desilu Playhouse, hosted by Arnaz himself, in the early part of 1959. Arnaz had wanted Van Johnson to play Eliot Ness, the leader of the crack federal team that was formed to bring down the mob, and, more specifically, Al Capone (Neville Brand). Johnson's manager-wife turned down the role, asking for more money, and so Arnaz turned to Robert Stack, who ended up earning icon status as Ness.
That initial two-parter was reissued for theatres under the title, "The Scarface Mob", and, loosely based on Ness' own memoir, told how Capone would eventually be brought down on tax evasion charges. It also introduced audiences to one of the more influential producers of the 60's & 70's, Quinn Martin, who would be elevated to executive producer for Untouchables. Martin, however, left after the second season, spinning off his own production company, which in turn would last nearly 20 years.
The series premiere, "The Empty Chair", centered on the "Enforcer", Frank Nitti (Bruce Gordon), who would return frequently during the series' 4 year run. Unfortunately for Gordon, a veteran character actor, the part also resulted in typecasting, leading to his last regular series gig, the gangster spoof, Run, Buddy, Run, in 1966. Two years later, Gordon would reunite with Stack to spoof their iconic roles on The Lucy Show, and the last time Gordon was seen, as far as I know, he was still in pinstripes, doing an ad for Canada Dry ginger ale. How ironic, no?
The Untouchables brought an Emmy Award for Stack after season 1, and Elizabeth Montgomery, 4 years before Bewitched, guest-starred in the season 2 opener, and was nominated for an Emmy herself. The supporting cast was seemingly changing on a regular basis. Anthony George & Jerry Paris left after season 1, and would land other gigs (Checkmate & The Dick Van Dyke Show, respectively) at CBS. John Beradino, who appeared in "Scarface Mob", was cast in Quinn Martin's 1st series, The New Breed, then shifted to daytime 2 years later in General Hospital. Newscaster Walter Winchell was the narrator, and he & Stack were among the few who were there from start to finish.
There's no mistaking Nelson Riddle's pulsing theme song, but after Martin left, Desilu tried out other producers, such as Leonard Freeman and Jerry Thorpe, and eventually hired Pete Rugolo to record a new version of the theme song in season 4. That, friends, would be the kiss of death.
Nearly 30 years after "Scarface Mob", director Brian DePalma and writer David Mamet brought The Untouchables to the big screen, with Kevin Costner as Ness, and Robert DeNiro as Capone, a far superior Capone than Brand's to be honest. This would lead to the series being revived in syndication in the 90's, with Tom Amandes as Ness. The new version lasted just a couple of years, largely because of the time lag in between the movie and the series being longer than the original.
Edit, 8/16/2020: "The Empty Chair" has been deleted. In its place is an excerpt from "The Frank Nitti Story":
If there was one criticism with Untouchables, it was in the negative portrayal of Italian-Americans, an issue addressed in season 1 when Nicholas Georgiade was cast as barber-turned federal agent Enrico Rossi, whose role would increase in the final season.