IIRC, "Roger" came about in the early days of voice-radio communication as the old-style phonetic alphabet version of "R" (in the modern phonetic alphabet, "R"

IIRC, "Roger" came about in the early days of voice-radio communication as the old-style phonetic alphabet version of "R" (in the modern phonetic alphabet, "R" would be "Romeo") ; the single letter R was a "prosign" abbreviation used in Morse-code telegraphy (as • — • or dot-dash-dot) to indicate "received and understood." [0] [0] https://en.wikipedia.org/wiki/Morse_code_abbreviations https://en.wikipedia.org/wiki/Morse_code_abbreviations