As Donald Trump addressed the crowds gathered at the Lincoln Memorial in Washington DC to celebrate the Fourth of July, a roly-poly balloon depicting the US President as an angry, orange, nappy-wearing baby flew nearby.

The Trump Baby blimp has become a familiar sight to see hovering above protesters unhappy with the President's policies and rhetoric.

But the caricatured balloon was not created by a discontent American — it was created in England.

Whose idea was it?

The blimp spans six metres in height. ( Supplied: Crowdfunder/Trump Baby )

The balloon was designed in 2018 by Matt Bonner and Leo Murray ahead of Mr Trump's first official visit to the UK in July.

The pair are part of a group that describes itself as anti-fascist art activists.

"We were looking for something that would literally rise up above the streets and make a bold statement," Mr Bonner told GQ.

"So that's where the balloon idea came in."

As for depicting Mr Trump as a baby, Mr Bonner said the concept was "self-explanatory".

"He's someone who famously throws toys out of his pram when he doesn't get his own way, so it's not the first time Trump has been depicted as a baby, but it just seemed like the perfect device."

How much did it cost?

In just 24 hours, the group crowdfunded more than $18,427 to make the structure and, after finding a manufacturer to create the massive inflatable, the idea became a reality and was flown over the UK Parliament during Mr Trump's first state visit in 2018.

This was the blimp inflated during Mr Trump's 2018 UK visit. ( ABC News: Roscoe Whalan )

Mr Murray said the aim was to "remind the President how unwelcome he is in this country".

"We're also, in a light-hearted way, trying to articulate the strength of feeling against Donald Trump and his politics of hate."

The blimp was heavily criticised by Mr Trump's supporters and politicians, including Nigel Farage, who said it was "the biggest insult to a sitting US president ever".

Mr Trump even told The Sun newspaper that the blimps made him feel unwelcome.

"I used to love London as a city. I haven't been there in a long time. But when they make you feel unwelcome, why would I stay there?" Mr Trump said.

For Mr Trump's most recent visit in May, the group said they would not fly the blimp unless they could raise 30,000 pounds ($53,723) for several UK and US charities.

So when the crowdfunding total shot past its goal to reach 37,000 pounds, the group got out the inflator once again.

And again for his state visit in 2019. ( AP: Matt Dunham )

Since then, replicas have flown all over the world, and are maintained by a group of "babysitters".

One of the babysitters, Max Wakefield, told Fortune that the blimps have travelled to Buenos Aires, Dublin, and Paris.

Mr Wakefield said that, deflated, it can fit into a suitcase, and that the group even have a smaller version for ground protests called Baby Trump Baby.

Why has the baby appeared for Fourth of July celebrations?

Members of the District of Columbia National Guard walk past the balloon. ( AP: Patrick Semansky )

For this year's Independence Day parade in Washington DC, the Trump Baby blimp was put up by anti-war organisation Code Pink to protest what it calls the President's co-opting of Independence Day.

Code Pink co-director Medea Benjamin said the organisation and its members "oppose the politicisation of July Fourth by President Trump".

"We think that he is making this about himself and it's really a campaign rally," Ms Benjamin said.

Mr Trump has become the first president in nearly seven decades to address a crowd on Independence Day. ( AP: Alex Brandon )

Mr Trump had ordered the Pentagon to stage military demonstrations, including a flyover of jets, helicopters and other aircraft.

Mr Trump also addressed a crowd of hundreds of thousands at the National Mall about "the future of American freedom".

Ms Benjamin said the balloon was a "great symbol" of how people felt about the President.

"He's erratic, he's prone to tantrums, he doesn't understand the consequences of his actions," she said.

The Museum of London is even working to acquire it

The museum announced in June that it was in negotiations with the creators to acquire the blimp as part of its permanent collection.

In a statement, a spokesperson said London had played host to many historic protests, from the Suffragettes to the anti-austerity marches, free speech and climate change rallies.

"[The blimp is] a recent symbol embodying public sentiment at a controversial moment in the capital's history," the statement said.

The ABC understands the negotiations are still underway.