Acting for Two: Martin Landau as the twins Dexter and Norman Paris in "Double Shock", one of the very few episodes where the real killer is unknown until the end. Dexter is the murderer, but Norman is also in on it.
Actor Allusion: Robert Costanzo (best known as Harvey Bullock from Batman: The Animated Series) has a cameo in "Columbo Goes to the Guillotine", playing a bar owner who happens to be a retired police sergeant. Costanzo was a police officer before he became an actor.
Actor-Shared Background: Columbo tells a police officer helping him in one search that "Three eyes are better than one," implying that Columbo has a false eye just like Peter Falk.
Dawson Casting: In "An Exercise in Fatality", Robert Conrad plays a 53-year-old fitness expert whose healthy lifestyle leaves him looking like he's in his thirties. Conrad actually was 39 at the time of filming.
Directed by Cast Member: Peter Falk directed "Blueprint for Murder" (given he was the show's only regular, it could hardly be anyone else).
Frequent guest star Patrick Mc Goohan directed several episodes as well, including three of the four he appeared in.
"No Time to Die" is an adaptation on the 87th Precinct novel So Long as You Both Shall Live, with Columbo taking the place of multiple 87th Precinct cops (in the novel Bert Kling's new wife Augusta is kidnapped on the day they're married, in this adaptation it's Columbo's nephew's wife who's taken).
"Undercover" is also an 87th Precinct adaptation, of the novel Jigsaw. Unlike the above, this version includes one of the characters from the 87th (Arthur Brown, who's also one of the cops investigating in the book).
Lt. Columbo is Italian-American, as was made a point of numerous times. Peter Falk is of Russian and Polish descent. Likewise, whereas Falk was Jewish, it was often hinted that Columbo is Catholic (at the very least, his own nephew's wedding is a traditional church-type wedding).
Hector Elizondo playing an Arabic national in "A Case of Immunity". Although Elizondo does arguably have the appropriate profile to fit such a person.
Jamie Lee Curtis had a brief cameo in season 5 as a waitress. Just earlier in that same season, Janet Leigh, her mother, played the killer.
It's also fun to play this with recurring actors throughout the movies. One person who plays either a random police officer or just a bystander in one episode might be the victim or accomplice in another. Sometimes, as with Dabney Coleman, a police officer in one and then the killer in another.
Both of the shrinks in Monk, Stanley Kamel and Hector Elizondo (Dr. Kroger and Dr. Bell). Elizondo was the murderous Suarian ambassador in "A Case of Immunity", while Kamel plays Tim, one of Congressman Paul Mackey's aides in "Agenda for Murder". The interesting thing is that you will recognize Kamel from his voice, and you see that he had hair at the turn of the 1990s that made him look a lot like 1990s Bruce Willis, but was mostly bald by the time Monk began.
They're not alone when it comes to actors who appeared in Columbo and Monk: Gena Rowlands appeared as Harold Van Wick's wheelchair bound wife Elizabeth in "Playback", and was Marge Johnson in "Mr. Monk and the Lady Next Door."
Johnny Cash murders his wife (and the girl he had an affair with) in "Swan Song".
Patrick McGoohan (#6 from The Prisoner and Drake from Danger Man) appeared in four episodes over the series, all of which he was the murderer. He was also the director of all of these and two others — these got him two Emmy awards.
Little Richard cameos as himself in "Murder of a Rock Star".
This trope is played in-universe in "Uneasy Lies the Crown" when Columbo questions the poker players to the alibi of the killer — Nancy Walker, Dick Sargent and Ron Cey all portray themselves.
In the final episode, "Columbo Loves the Nightlife", Jorge Garcia briefly appears in a blink-and-you'll-miss-it moment as a bouncer, one year before he'd become much better known to television audiences playing Hurley on LOST.
Non-Singing Voice: In "Murder of a Rock Star" actress Cheryl Paris plays the role of Marcy Edwards, the murder victim and former rock singer. "Closer", the song played in the episode was actually sung by Shera Danese, a frequent guest star of the series and Peter Falk's wife. Partly subverted as there was no actual dubbing involved, since we only hear the song played on stereos with no live performance. Weird, considering that Shera Danese appears in the episode playing Hugh Creighton's assistant/partner Trish Fairbanks.
Playing Against Type: Most of the guest stars played murderers, and many of them carried their typical screen personas into the role. Others did no such thing:
Dick Van Dyke, who usually plays the comic relief in musicals like Mary Poppins or Chitty Chitty Bang Bang, as well as a comedy writer on the The Dick Van Dyke Show, played a particularly ruthless Paul Galesko in "Negative Reaction" — a henpecked photographer who shoots his wife and a recently-released prisoner that he'd hired to run small errands, in an attempt to make it look as if the other man was the kidnapper.
Similarly, George Wendt played a humorless, bitter killer, in stark contrast to the silly, self-deprecating shlemazel he played in Cheers.
Janet Leigh, perhaps most famous for playing the murder victim in Psycho, getting to play the killer in "Forgotten Lady".
Bruce Kirby Jr. and Sr. in "By the Dawn's Early Light".
Peter Falk and Shera Danese. They were married shortly after her first appearance in the series and remained so until Falk's death.
Catherine McGoohan, Patrick McGoohan's daughter, plays the funeral home assistant opposite her father in "Ashes to Ashes".
Katey Sagal appeared in a small role in "Candidate for Crime", which was directed by her father, Boris.
Referenced By: A number of other shows have made shout outs to Columbo as well.
In Remington Steele a running joke has Remington referring to old movies to help him find clues to current cases. In one episode this is flipped, and his partner Laura Holt refers to TV series, specifically the first William ShatnerColumbo episode.
In an episode of Bosom Buddies, Henry dresses and acts like Columbo as part of a sting to catch a bad guy wronging Amy.
In an episode of The Odd Couple, Murray the Cop goes undercover to spy on Felix's ex-wife and dons a raincoat.
Murray: Whatta you think Oscar? Do I look like Columbo? Oscar: [You look] more like Dumbo.
Monk is also fond of taking things from Columbo. The episode "Mr. Monk and the Red-Headed Stranger" combines elements of at least four different Columbo episodes. Monk is also compared to Columbo on multiple occasions.
"Mr. Monk and the Red-Headed Stranger" blends the plots of several Columbo episodes: 1) The fact that the bullet hole in Sonny Cross's jacket does not match the position of the bullet hole in the body determines whether or not the victim was on good terms with the killer comes from "Fade in to Murder"; Johnny Cash played a sympathetic country/gospel singer accused of murder in "Swan Song", while in this episode, it's Willie Nelson playing himself getting framed for murder (Stottlemeyer makes a remark about Cash's performances at Folsom by saying that Willie Nelson will soon be performing "live from Folsom Prison"). And there is a blind witness with a twist (Mrs. Mass), just like in "A Deadly State of Mind".
In "Mr. Monk Is on the Run, Part Two", Natalie realizes that Monk is alive when she sees a newspaper article about the "Car Wash Columbo", a (supposedly) Hispanic car wash man who recently helped the local police solve the hit-and-run death of a highway safety worker single-handedly. Monk has faked his death and Stottlemeyer has made it seem that he's dead, so this incident ends up blowing his cover. Of course, Natalie is not happy to find that Stottlemeyer has known about this the whole time and was lying to her (when in truth, he was trying to keep Monk away from Sheriff John Rollins, the guy who framed him).
In "Mr. Monk Buys a House", 'Honest' Jake Phillips refers to Monk as Columbo. Hector Elizondo, who debuts as Dr. Bell in that episode, played Hassan Salah, a murderous diplomat in "A Case of Immunity". The plot is also like the episode "Undercover", in that a string of new murders occurs that is tied to an old unsolved bank robbery.
Some bits of "Mr. Monk Goes Back to School" are based on "Etude in Black," such as the fact that the murder victim, Beth Landow, is much like Jennifer Welles: she is pregnant, she is having an affair with the killer (Derek Philby, vs. Alex Benedict), and her death is made to look like a suicide.
Two episodes, "Mr. Monk and the Miracle" and "Mr. Monk and the End," bear some elements of "Requiem for a Falling Star," especially the latter, which features a string of murders that are tied to a body buried under a sundial, and features a killer who won't move out of his current house because of said body.
In "Mr. Monk Gets Lotto Fever", a crucial clue that an apparent suicide was murder is that a contact lens case is found with only one lens in it, and the other contact lens is found on the victim's body. This is the same clue that was used by Columbo in "Murder, a Self Portrait" to determine that a drowning death was actually murder.
In "Mr. Monk Is Underwater," Commander Whitaker uses a cigarette as a fuse for a firecracker to give himself an alibi, by fooling people into thinking that an apparent suicide victim shot himself while the commander and the senior officers were banging on his cabin door, with the firecracker simulating the sound of a gunshot, just like Nelson Hayward in "Candidate for Crime".
In one of the flashbacks to Monk's childhood in 1972 in "Mr. Monk and Little Monk", one of his classmates mockingly calls Monk "Columbo".
Science Marches On: Most of the schemes the killers use to establish their alibis, disguise the cause of death or change the apparent time of the murder would today be handily disproved by modern forensic science, without any need for Columbo's unique investigatory techniques.
In "Double Exposure", both the killer's method of luring the victim to his doom and Columbo's plan to catch him depend on the use of Subliminal Advertising, which has since been totally debunked.
In "Agenda for Murder", Columbo proves the killer's guilt because he took a bite from the victim's sandwich and no two bitemarks are supposedly alike. This theory was debunked in Real Life in a notorious case where an innocent man was convicted of murder for precisely the same reason only to be later cleared when the real killer was caught. It turns out two people can have identical bitemarks.
Technology Marches On: A number of episodes center around a killer making inventive use of the latest technological marvels, and relying on the police failing to know how they work. A contemporary viewer will get a few chuckles out of:
"Ransom for a Dead Man" — Leslie Williams shoots her husband and dumps his body, then uses a dictaphone recording to fake his kidnapping.
"Fade in to Murder" — Ward Fowler (William Shatner) using a VCR to fake an alibi by time-delaying a baseball game so that his guest will vouch for his location at the time the game was broadcast.
"Butterfly in Shades of Gray" — Fielding Chase (also Shatner) who has killed Gerry Winters and made it look like Winters was killed while talking to Chase on the phone. Chase makes a 911 call on his car phone once he leaves the scene, and makes it seem like he called 911 shortly after leaving his own house. His story falls apart when Columbo reveals that Chase could not have called 911 from where he claimed he was, because said location happens to be in a mountainous area where there is a dead zone and it is impossble to get a phone signal.
"Columbo Cries Wolf" — The victim's body is revealed when Columbo calls her wrist pager.
"An Exercise in Fatality" — Milo Janus hides his location by making a call from multi-line phone system.
The final episode, "Columbo Likes the Nightlife", has the killer write out a fake suicide note on the victim's computer. It is easily discovered to be fake when Columbo gets immediately suspicious, has the forensics person check the keyboard and finds several keys have no prints on them.
"Playback"... oh wow... Harold Van Wick's got an in-house security system complete with cameras, microphones and a live feed to the guard house, plus a film room to record everything. A digital watch that prints the time in bright LED numbers. Doors that can open and close by clapping or other loud noises (Van Wick's wife is in a wheelchair). A wheelchair elevator for the staircase. All of it could be considered mundane by today's standards but for the time the episode was made, certainly high tech.
Throw It In: "Just one more thing..." In addition, many of Peter Falk's absent-minded moments were ad-libbed. He figured that if they were all scripted, it would be harder for his fellow cast members to react genuinely. So, in the middle of scenes with the suspect, Falk would unexpectedly start fumbling around for his shopping list or pretend to forget what he was talking about. The standard perp expression that seems to say "What is with this guy?" is thus usually very real.
Peter Falk wanted Patrick McGoohan to play the role of Findlay Crawford in "Murder with Too Many Notes", but McGoohan had acted in the previous Columbo film, "Ashes to Ashes", so McGoohan declined and the role went to Billy Connolly instead, with McGoohan directing (he also co-wrote the script).
Steven Bochco wrote the script to "Uneasy Lies the Crown" in 1973, which if it'd been made would've been a part of season 2 or 3. Peter Falk turned it down at the time, only to make it later in 1990. One has to wonder who would've been the killer if it'd been made in 1973.