Columbo (1971–2003) 
With his rumpled raincoat, ever-present cigar, bumbling demeanour and Sherlock Holmesian powers of deduction, disarmingly polite homicide detective Lieutenant Columbo took on some of the most cunning murderers in Los Angeles, most of whom made one fatal, irrevocable mistake: underestimating his investigative genius.
Showing:
Columbo: An Exercise in Fatality Season 4, Episode 1
In which we learn the importance of using safeties. Always lift with a buddy. [more inside]
Columbo: Negative Reaction Season 4, Episode 2
In which Dick Van Dyke is revealed to be the villain we always knew he was.
Columbo: By Dawn's Early Light Season 4, Episode 3
A sweaty head of a military academy, played by Patrick McGoohan, will not put up with his institution being turned into a co-ed junior college. [more inside]
Columbo: Fade in to Murder Season 6, Episode 1
Columbo investigates the death of a TV producer and immediately gets the attention of actor and murderer Ward Fowler (William Shatner), who plays a detective on TV. Fowler immediately sees through Columbo's aw-shucks act ("Why don't we stop pretending that I'm brilliant and you're simple for one moment?") and is among the least visibly rattled of Columbo's opponents. Episode is currently free to stream in the US via Amazon's Freevee (formerly IMDbTV), as is Columbo in general.
Columbo: Dead Weight Rewatch Season 1, Episode 3
In which Eddie Albert (Oklahoma!, Dreamscape, Green Acres) is a charismatic general who shoots a military contractor, and Suzanne Pleshette (The Bob Newhart Show, The Birds) is the sole witness. Boating ensues.
Columbo: Death Lends a Hand Rewatch Season 1, Episode 2
When the CEO of a private detective agency threatens the wife of a publisher with blackmail and she threatens to expose him, he accidentally kills her.
Columbo: Murder By The Book Season 1, Episode 1
A member of a mystery-writing team goes missing under mysterious circumstances. Directed by Stephen Spielberg. In 1997 TV Guide ranked this episode number 16 on its '100 Greatest Episodes of All Time' list.