But Donald Trump is not just any leader.
We look at the make-up of the presidential entourage.
"There will be no alliance more important in the years ahead", she said.
On Friday, demonstrators are expected to gather near Chequers, the Prime Minister's country residence, where May and Trump will hold a working lunch.
Protests are also planned in Scotland when he travels to play golf at his Trump Turnberry course.
A campaign is also underway to get "American Idiot", a 2004 song by the U.S. punk rock band Green Day, to the top of the UK Singles Chart.
The on-off visit of Donald Trump to the United Kingdom is finally happening - but that doesn't mean the controversy has stopped.
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The aircraft has 4,000 square feet of floor space, including a Presidential suite with a large office and conference room, a medical suite that can be used as an operating room and two food preparation galleys that can feed 100 people at a time. He's not coming here for himself.
Some British citizens are even more distressed about Trump than they are about the U.K.'s own feverish political turmoil. It was during that trip to Washington that she invited him to the UK. "I was happy when Obama did it". He also suggested that he might speak to his "friend" Mr Johnson, who had been due to attend a dinner with the president and business executives on Thursday evening.
She says they have "turned a blind eye" to the situation.
But the red carpet treatment is likely to be overshadowed by massive protests planned by Britons opposed to Trump's presence.
"I think it's amusing". "I believe that the people in the UK, Scotland, Ireland, as you know I have property in Ireland, I have property all over, I think that those people they like me a lot and they agree with me on immigration", he said.
The US President touched down in London Stansted Airport, Essex, at 1.50pm BST with his wife, First Lady Melania Trump, after arriving from the North Atlantic Treaty Organisation summit in Brussels.
Mr Morgan, the forthright journalist and broadcaster, hit back and questioned why the London mayor had not been so vocal over the visit of controversial Turkish President Recep Erdogan. The UK's speaker of parliament made clear that Trump, because of his values, would not be invited to address MPs.