On Sunday, Donald Trump caused outrage with a tweet that appeared to contain a repurposed post by a Reddit user: a gif showing the president wrestling to the ground a figure with a CNN logo for a head.

Trump’s tweet resurfaced questions about his conduct in office and the increased danger of attacks on journalists as the president persistently criticises the mainstream media.

A year to the day after Trump tweeted antisemitic imagery in a message attacking Hillary Clinton, his Sunday tweet also raised questions about how and why Trump and his team source the images used in his social media posts.

On 2 July 2016, Trump issued a tweet that showed Clinton with piles of money and a six-pointed star. In the face of intense criticism and reports the image had been sourced from an internet message board used by white supremacists, the tweet was deleted and reissued with a circle instead of the star, which Trump claimed had been meant to represent “a sheriff’s star, or plain star!”

A year on, the Reddit user who said he created the image on which Trump’s CNN-bashing tweet appeared to be based, was found to have posted under the name “HanAssholeSolo”, and to have been the author or propagator of racist, antisemitic, Islamophobic and misogynistic comments and images.

The footage in HanAssholeSolo’s gif and Trump’s tweet was taken from Wrestlemania XXIII, in 2007, during which Trump “attacked” WWE promoter Vince McMahon. HanAssholeSolo posted the gif version of the clip on Wednesday. On Sunday, the user quickly claimed credit.

“Holy shit!!” HanAssholeSolo wrote at 11.11am. “I wake up and have my morning coffee and who retweets my shitpost but the MAGA EMPORER [sic] himself!!! I am honored!!”

Three hours earlier, HanAssholeSolo had been taking part in a discussion on the “Reddit pics” section of the website. Another user had posted a photo of a banner which said: “Totally failed at life? Then why not blame a foreigner.”

HanAssholeSolo wrote: “In America it’s blame the white person.”

On Monday, the White House did not immediately respond to a request for comment. In the face of condemnation from Republicans, Democrats and free press groups, Trump has not commented on his Sunday tweet.

HanAssholeSolo also did not immediately reply to a request for comment. The user appeared to have deleted a series of posts after Trump tweeted the CNN video, but screengrabs collected by Quartz and other outlets showed a series of disturbing remarks.

HanAssholeSolo has repeatedly railed against the perceived mistreatment of white people and denigrated other races using shocking and abusive language.

In May the user took part in a discussion, which appears to have been deleted, and described someone as a “nigger” before asking: “Explain to me why a weekend doesn’t go by where 80 of you fucking moon crickets aren’t shooting each other down in Shitcago [Chicago]? Why you dumb fucking nignogs can’t attend a rap concert without someone being shot up?”

He went on to make further offensive remarks about black people in the same thread.

In reply to another poster, he wrote: “500,000 dead Muslims is a good start. Kill the rest and I’ll be impressed. Good keep up the good work until the last Islamic piece of shit is wiped from the planet.”

In other posts, HanAssholeSolo used the terms “goatfucker”, “faggot” and “retard”. On 13 June, he posted an image showing dozens of CNN hosts and employees, each with a star of David attached and with the caption: “Something strange about CNN … can’t quite put my finger on it.”

An examination of HanAssholeSolo’s internet history offered some clues about his identity.

HanAssholeSolo has identified as as a fan of the Half-Life series of video games, an ex-smoker and a military veteran. The user appears to live in Tennessee and to have a permit to carry a concealed weapon.

The username, based on the Han Solo character played by Harrison Ford in the Star Wars films, would suggest a science fiction fan. In May, HanAssholeSolo joined a Reddit conversation about Star Wars Episode IV: A New Hope.