The letter has a long historical association with slumber, surprisingly. Though it is difficult to cite when it became used colloquially, in writing, we can trace it at least back to The Writings of Henry David Thoreau: Journal 1837-1846, who wrote about the low buzz of insects: “The dry z-ing of the locust is heard….” And over the years, that buzz merged with snoring, though it may have taken 20th-century comics to cement the association in popular culture. As early as 1903, in a comic strip called The Katzenjammer Kids, the letter is seen flying from a character’s head as he rests oblivious to the titular kids’ antics (creator Rudolph Dirks was also the first to express dialogue in speech balloons). Sleep and snoring became virtually interchangeable in the language of comics, and a new standard had been agreed upon. It became formalized by the American Dialect Society in 1918, and popular idioms soon followed, such as “catch some z’s.” The letter became permanently linked to everyone’s favorite biological imperative with time.
And why did they choose this letter in the first place? Here it becomes more revealing to speculate, as one unifying answer has been lost to time. Most regularly assumed is that the letter ‘z’ is the most proper onomatopoeia to represent the sound of a snore. (Maybe because sporadic gargles and heavy breathing aren’t universally translated.) Snoring is often referred to as “sawing logs,” given the similar sounds at play and possibly just the physical activity of sawing as a means to wear yourself out before bed. And just for fun, imagine a sawing motion. What letter’s shape does it most closely resemble in its back-and-forth, zig-zagging rhythm? Hmm...
Another popular term for sleep is snooze. The ‘z’ resting in that word may have played an influencing factor in its linguistic synecdoche. And where does ‘z’ land in the alphabet? Traditionally, where does sleep land in one’s day? Ah! The rabbit hole of correlations can be endless the longer you dig into it, and the longer you dig, the more likely you are to doze off. Hey! There’s another! And even though other cultures and languages have their own representations of snoring (Korean: “DE REU RUNG”; Japanese: “GU GU”; French: “RON PCHI”), ‘z’ is still commonly used worldwide.
Perhaps all of these signify it was simply Z’s destiny to represent the wide world of sleep. Perhaps its fate was inescapable. One thing’s for certain: No letter could do the job better. And now, with one less nagging question to keep you up at night, you can focus on catching some zzz’s yourself.