The US president tweeted the picture on Wednesday morning without a caption or a single word of explanation.
It shows his head superimposed onto the body of the famous fictional boxer, played by Sylvester Stallone in a string of successful films.
More than 500,000 likes later, people are still trying to work out what it’s all about.
Many have tweeted unflattering photos of Mr Trump in response, pointing out the obvious difference between the chiselled Stallone in his prime and the flabby, obese 73-year-old president.
Among various mock-ups doing the rounds is a picture from Rocky IV, showing House Speaker Nancy Pelosi delivering a vicious punch to Mr Trump (whose face is on the the Russian character Ivan Drago).