Twitter and Facebook repeatedly mishandled Donald Trump as he pushed baseless claims, including his assertion that US presidential election he lost was rigged, Wikipedia founder Jimmy Wales told AFP.

The two social media giants indefinitely suspended Trump after his supporters stormed the US Capitol on January 6, an attack on the seat of democracy that on Wednesday led to Trump's second impeachment.

Wales told AFP in an interview to mark Wikipedia's 20th anniversary on Friday that responsibility for the unprecedented events in Washington rested "100 percent at the feet of Donald Trump".

But he said Twitter and Facebook had consistently "struggled with misinformation, disinformation" peddled by the firebrand former New York real estate tycoon who is due to leave office next week.

"With Donald Trump, they did a poor job of dealing with him for a very, very long time," Wales said. "He was clearly spreading disinformation, he was clearly being abusive to people."

- Eyeballs v knowledge -

In the 20 years since it was founded, Wikipedia is now one of the most popular websites in the world, with in excess of 55 million articles in 300 languages. It is read more than 15 billion times every month.

It is also, as Wales first envisaged, "a world in which every single person on the planet is given free access to the sum of all human knowledge".

The internet entrepeneur's decision in 2003 to make the site non-profit is one reason he believes Wikipedia has not faced the same backlash and difficult decisions as Twitter or Facebook.

"They (social media platforms) have a business model that says, 'We need as many eyeballs as possible, we need as many page views as possible'," the 54-year-old said.

"Now it's also damaging for their brand. So they have to deal with that. But I think they're going to struggle."

Facebook and Twitter have become closely associated with the deeply divisive culture wars in the United States and the spread of misinformation worldwide.

In contrast, Wikipedia is considered one of the last examples of early web utopianism, supporters say.

In the early 2000s, though, falsehoods and user vandalism on Wikipedia sparked a debate on web regulation.

But the online resource is now more likely to be held up as an example of the best the internet has to offer, the American-British entrepreneur says.

"I always say, we were never as bad as they said we were and we're not as good as they think we are," he said.

"But we still know Wikipedia isn't perfect. We still have a lot of work to do."

- 'Building it to last' -

Wales is also aware Wikipedia is fundamentally different from social media platforms.

"We have a very clear mission to create an encyclopaedia. So everything we do we judge against that standard," he said.

"(That is) a very different mission statement from a social network that says, come and post what you think, post your opinions.

"Because the truth is, lots of people have really horrific opinions."

Wales admits that Wikipedia still has challenges to overcome, and has faced questions about the diversity of the thousands of "Wikipedians" -- the community of editors and administrators who keep the site running.

In 2021, Wikipedia will implement a uniform code of conduct with corresponding sanctions against insults and harassment, which have targeted minority groups within the community in the past, across all 300 of its different language versions.

Wales said formulating the code of conduct "did take longer than it should have", but that was because the community was so large "it takes a long time to work through things and get buy-in and understanding".

The goal for the next 20 years, though, will be remarkably similar for the first two decades.

In 2006, Wales set the goal of having 100,000 entries in Wikipedia for every language with more than one million speakers.

"We're still at least 20 years from that," he said.

He hopes, ultimately, that he has created an institution that will endure, like Britain's Oxford University, the oldest in the English-speaking world, which can trace its roots back to the late 11th century.

"We really do focus on how do we build an institution that can last," said Wales. "We really want to be that type of thing in society for a long time to come."