Duolingo is a language-learning platform released in 2009 that features both a website & an app. The meme of Duolingo was created when users noticed how incessantly the app would send out notifications if you miss a class. They began making memes where the Duo the Owl would threaten them if they hadn’t used the app in 24 hours.
Duo was known for cussing.
Duolingo first officially recognised the meme on April 1st of 2019, where they released a video for a "Duolingo Plush" which would follow you around and remind you of your lessons.