Carl the Hedgehog refers to an exploitable image of a hedgehog named Carl paired with the text explaining that the image will only be posted once. The image spawned a series of derivative posts featuring Carl coming back for various reasons and updates on his further life.
On October 1st, 2014, Pixabay user amayaeguizabal uploaded several photographs of a hedgehog sitting on a porch.
On February 28th, 2019, Redditor Lawvamat posted a cropped image of the hedgehog to me_irl subreddit, writing what the hedgehog’s name was Carl and that he would only be posted once, and urging other Redditors to say hi. The post followed the trope of It Is Wednesday, My Dudes and Reginald posts and gained over 48,800 upvotes in one week.
On March 1st, the image was reposted by popular Instagram meme account i_have_no_memes96_v2 (326,000 likes gained in one week), along with several other notable pages.
In the following week, multiple posts about Carl were posted on /r/me_irl subreddit and on Instagram, with many notable versions made by Instagram user dinopox (examples shown below).