The labarum (Greek: λάβαρον) was a vexillum (military standard) that displayed the "Chi-Rho" symbol ☧, formed from the first two Greek letters of the word "Christ" (Greek: ΧΡΙΣΤΟΣ, or Χριστός) — Chi (χ) and Rho (ρ). It was used by the Roman emperor Constantine I. Since the vexillum consisted of a flag suspended from the crossbar of a cross, it was ideally suited to symbolize the crucifixion of Christ.

The etymology of the word labarum is unclear; it is perhaps to be derived from Latin /labāre/ 'to totter, to waver' (in the sense of the "waving" of a flag in the breeze). Other proposals include a derivation from Celtic llafar ("eloquent"), from the Latin laureum [vexillum] ("laurel standard") or from ancient Cantabri dialect labaro ('four heads') (in modern-day Basque the word is lauburu, with the same meaning), an ancient celtic symbol taken by the Legions during the Cantabrian Wars.

Later usage has sometimes regarded the terms "labarum" and "Chi-Rho" as synonyms. Ancient sources, however, draw an unambiguous distinction between the two.

The Shadow is a collection of serialized dramas, originally in pulp magazines, then on 1930s radio and then in a wide variety of media, that follow the exploits of the title character, a crimefighting vigilante in the pulps, which carried over to the airwaves as a "wealthy, young man about town" with psychic powers. One of the most famous pulp heroes of the 20th century, The Shadow has been featured in comic books, comic strips, television, video games, and at least five motion pictures. The radio drama is well-remembered for those episodes voiced by Orson Welles.

Introduced as a mysterious radio narrator by David Chrisman, William Sweets and Harry Engman Charlot for Street and Smith Publications, The Shadow was fully developed and transformed into a pop culture icon by pulp writer Walter B. Gibson.

The Shadow debuted on July 31, 1930, as the mysterious narrator of the Street and Smith radio program Detective Story Hour. After gaining popularity among the show's listeners, the narrator became the star of The Shadow Magazine on April 1, 1931, a pulp series created and primarily written by the prolific Gibson.