Martin Landau essayed double roles in the pilot and "Wheels."
In "Shock" guest star James Daly played a kidnapped U.S. envoy, the enemy agent impersonating him and Dan Briggs disguised, thanks to Steven Hill's difficulties.
When Leonard Nimoy replaced Martin Landau as the disguise expert, he played his regular role of Paris and the Big Bad in "The Choice," and Paris, a double of a deceased premier and said premier (in pictures), plus the "Robot" of the title. There were also several times when he played minor roles in disguise and the audience had no idea it was him.
Shannon went undercover in several roles that required her to sing, which allowed Jane Badler to showcase her talent as a singer.
In "Gunslinger", Jim Phelps remarks that he used to be pretty good with a sixshooter and does a few Gun Twirling tricks to the admiration of his teammates. The filming makes it obvious that actor Peter Graves (who cut his acting teeth in westerns in the 1950s) is doing his own twirling.
Casting Gag: The 80's sequel series starred Greg Morris's son (Phil Morris, perhaps best known as Jackie Chiles) as Barney Collier's son.
Creator Backlash: Paul Playdon, script consultant in seasons three and four, was so ashamed of his own "Time Bomb" (as were many who worked on the episode) that he actually left the show. (While he contributed "The Catafalque" in season five and has story credit on season six's "The Tram," he never returned as a staff member.)
The Danza: Subverted. Bruce Geller wrote Martin Landau's part with the actor in mind, going so far as to name the character "Martin Land" in the pilot script. Landau said he was honored, but requested the name be changed, which it was to "Rollin Hand". Played straight in "The Tram," with Victor French as Vic Hatcher (although even then it was nearly averted, as French replaced originally cast Keenan Wynn).
Defictionalization: According to the book The Complete Mission: Impossible Dossier the government contacted the producers to find out how they created a tiny hovercraft-like device that was (in show) controlled by remote control and sent down a shaft, somehow missing the somewhat obvious strings that were actually controlling the gizmo.
The self-destructing CDs seen in the 1980s revival series appear to act like DVDs - even though DVDs weren't introduced until the 1990s.
They were meant to be miniaturized laserdiscs (video discs that were read using laser like a CD, but were the size of a long-play record), which existed since the mid-80s.
In the episode "Robot" Leonard Nimoy plays his part under heavy make-up. This allows Paris to rip off his face mask in one take instead of the standard 'mask actor starts to take off face, cutaway to something else, cut back to IMF agent removing last bits of latex' routine.
At least in the first season, Martin Landau often played (with similar amounts of make-up) the people Rollin Hand was called on to impersonate.
Edited For F/X: When US cable channel F/X ran the series, bits with Briggs/Phelps giving counter-statements to agents in order to gain access to the recordings were removed, with the Tape Scenes beginning with Briggs or Phelps turning on the devices to hear the assignment. Other than that, episodes were presented edit free.
Fake Nationality: Israeli-born Nehemiah Persoff played the Big Bad three times: once as an Arabian, once as a Latin American, and once as an Eastern European.
The team adopt numerous ones in-universe, but the What the Hell Is That Accent?-worthy "Australian" one Paris puts on in "Chico" is notable because it's meant to be fake, as part of a persona which the week's Big Bad is supposed to unmask as fake, as part of the IM Force's plan.
Barbara Luna (from New York City) played a Latin American and an Asian in the original series, and a Latin American Big Bad in the revival.
The Merch: Record albums of the seriesnote although actual music from the show, as opposed to re-recorded versions, would not be released until 1992, as well as a few 'Young Reader' type books. Published by Whitman, The Money Explosion was particularly good. Near the end of the run, Paramount was considering the idea of MI branded tape recorders, but nothing came of the idea. There was a game for the NES released in time for the revival.
Non-Singing Voice: Averted by Barbara Bain in "Illusion" (the three songs she sings here were written for the show, and can be heard on La-La Land's multi-disc set that came out in 2015), Lesley Ann Warren (who had musical experience before [and after] her stint on the series) in "Flip Side," Greg Morris in "Blues" and Lynda Day George in "Trapped." And by Lynn Kellogg, an actual professional singer, in "The Martyr."
Possibly also Terry Markwell as the 1988 revival's Casey Randall whose character is killed off after only a dozen episodes.
Real-Life Relative: In the revival, Barney Collier's son Grant was played by Greg Morris's son Phil. Greg reprised his role as Barney in three episodes of the revival ("The Condemned" and "The Golden Serpent" parts 1 and 2).
Recycled Script: Done out of necessity in the revival series due to a writers' strike, but it was resolved early enough that only a handful of episodes ("The Killer," "The Legacy," "The Condemned" and "The System") were outright recycled from the original show.
Similarly Named Works: Both the original and the revival have an episode called "Submarine" - but unlike the episodes listed in Recycled Script above, the revival's "Submarine" is not a remake.
Technology Marches On: They went from tapes in the original 60s series to miniature compact discs in the 80s revivial. Likewise, in Jim's apartment, he uses a TV with a remote control to view the dossiers of agents and his table opens to reveal a computer with hard CD-type drives that were fancy for 1988. He wistfully goes, "Time does march on." The keyboard and remote then used to choose, then "accept" agents. Once Grant's selected, though, Jim has his team of four then, and another press of the remote finalizes them as "Mission Team."
Sid Haig, for example, was in the show no fewer than nine times, ranging from "Driver #1" to The Dragon to the Big Bad.
Lee Meriwether guest starred as a kidnap victim in a Season 3 episode, then was one of the femme fatale team members in Season 4.
Since M:I shared the Desilu/Paramount soundstages and some production personel with Star Trek, it should come as no surprise that William Shatner guest starred twice as a Big Bad ("Encore" and "Cocaine" - sadly for Star Trek fans, both came after Leonard Nimoy's tenure as an IMF agent... although the latter episode did reunite him with Barbara Anderson, alias Lenore Karidian from "The Conscience Of The King") and George Takei as an IMF member ("The Carriers"). Leonard Nimoy became an Suspiciously Similar Substitute of Martin Landau's character — four years after Landau had turned down the role of Mr Spock for Star Trek's first pilot "The Cage" in 1965. Herb Solow was production manager for both shows. Ricardo Montalban (Khan Noonien Singh) played a season one Big Bad, who was one of the only villains to be directly killed by the IMF team.
Going in the other direction, Robert Johnson, the mysterious voice on the MI tapes, provided uncredited voice work on at least two Star Trek episodes -the unaired pilot "The Cage" and the episode "The Gamesters of Triskelion". On the latter episode he provided the voice of "Provider #3", a disembodied brain in a container which engaged in an often quoted/parodied discussion about betting on the survival of Kirk & Company at hand to hand combat ("I'll bet 2,000 quatloos on the newcomers!") Johnson also voiced a few aliens on The Outer Limits (1963).
In at least one case, some alien artwork featured in an episode of Star Trek was actually the discarded protective styrofoam piece that housed an M:I prop tape recorder spraypainted orange and green.
One of Star Trek's infamous gag reels makes use of the Mission: Impossible theme music.
In Universe Example: Rollin Hand shows up in in a few photos with different names.
Barbara Luna is one of the few people to appear in the original (twice, as the title character in "Elena" and as an IMF agent in "Time Bomb") and the revival ("The Fortune," as a dictator's evil wife and killer of Casey Randall).
Disowned Adaptation: Fans and cast members of the original TV series strongly disliked the first film because it made Jim Phelps the villain. Peter Graves was offered the part of Phelps in the movie, but turned it down in disgust.
Unintentional Period Piece: The first movie obviously intended to be a "Mission Impossible about the new digital era", with its emphasis on computers, hacking, sensitive digital information and constant references to modems. Instead, the movie ironically traps itself in the 90s, with shots of Usenet, floppy disks, and massive laptops, things that the internet and computer technology left behind at almost light speed (plus that weirdly dated moment where a group of agents attempt to determine whether a disk had a tracking device in it or not by putting a digital thermometer on top of the exterior disk drive reading it).
The novelization identifies the device not as a thermometer but as an RF meter, detecting if any radio waves are coming from the disk. But there's nothing in the movie to identify what the gadget is.
What Could Have Been: According to Martin Landau, in an earlier treatment for the first film the original plan was to bring back the entire original cast of the TV series just to kill them all off in the first act, which was changed instead to wipe out the current team when the original cast members refused to come back. Considering how may fans reacted negatively to the change regarding Phelps in the first movie, one can only imagine how they would have responded had this plot happened.