The 'Sleep Tight Pupper' meme features an image of a small, white dog—typically identified as a Maltese or similar breed—snugly tucked into a tiny bed with blankets. It rose to prominence around 2015 on platforms like 4chan and Reddit, often accompanied by 'immune' style text claiming that users must reply with the phrase to ensure a good night's sleep. While it began as a variation of internet chain letters, it has since transitioned into the 'wholesome meme' genre, used widely to express comfort, coziness, or to wish followers a peaceful night. The meme is celebrated for its pure aesthetic and the lighthearted, low-stakes superstition surrounding the original 'reply to this' format.