Columbo's first name (from Wikipedia):
When Columbo is explicitly asked if he has a first name in season 4 episode By Dawn's Early Light, he just dispassionately answers back that he does, but the only person who uses it is his wife. In the season 12 episode Undercover, Columbo is asked once again what his first name is, to which he emphatically answers, "Lieutenant," a sentiment echoed by actor Peter Falk and creators Richard Levinson and William Link.
However, in the 1971 episode "Dead Weight", when Columbo introduces himself to General Hollister the audience is shown a brief close-up of Columbo's badge and warrant card, complete with signature, which appears to read "Frank Columbo". The same ID badge and warrant card is seen in numerous other episodes, and the signature "Frank Columbo" is clearly visible in the season 5 episode "A Matter of Honor".
Universal Studios, in the box set of seasons 1–4 under their Playback label, included a picture of Columbo's police badge on the back of the box, with signature "Frank Columbo" and the name "Lt Frank Columbo" in type. This appears to be a different badge from the one seen in "Dead Weight", with a different signature.
The "Philip Columbo" myth
Several sources cite the lieutenant's name as "Philip Columbo", variously claiming that the name was either in the original script for Prescription: Murder, or that it was visible on his police badge. For instance: a rumor that Columbo's first name is actually "Peter" has been denied by the star: "if he has a name at all," says Falk, "it is 'Philip,' which was the name used in the original story, Prescription: Murder." Peugeot ran an advertising campaign that mentioned "Lt Philip Columbo" as the most famous driver of the Peugeot 403 convertible.
The name "Philip Columbo," was, in fact, invented by Fred L. Worth, in whose book, The Trivia Encyclopedia, the fictitious entry about Columbo's first name was actually a "copyright trap" – a deliberately false statement intended to reveal subsequent copyright infringement. Ultimately, however, Worth's ploy was not successful. In 1984, he filed a $300 million lawsuit against the distributors of the board game, Trivial Pursuit, claiming that they had sourced their questions from his book, even to the point of reproducing typographical errors contained in the book. Worth's suit revolved around the use of the name, "Philip Columbo", included in a game-question about Lt Columbo. The makers of Trivial Pursuit did not deny that they sourced material from Worth's book, but argued there was nothing improper about using the book, as one of a number of other references, in the process of building game-questions. The judge agreed, ruling in favor of Trivial Pursuit, and the case was thrown out.