United States President Donald Trump is set to meet Russian President Vladimir Putin in Helsinki tomorrow in the first official meeting between two men who have had an interesting on-off "relationship" over the years.

From trading admirations to clashing on Syria and trade, the two powerful leaders have formed what has been described as a unique "bromance" all while investigations into Russia's alleged meddling in the 2016 US election are ongoing.

The two leaders met on the sidelines of the G20 and Asia-Pacific Economic Cooperation (APEC) summits, and Mr Putin said the pair speak "regularly" on the phone.

But now, on the eve of their first official summit, let's take a look back at the best bits of the Trump-Putin "relationship".

Miss Universe 2013 — a friendship blossoms

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Before he was donning Make America Great Again caps or putting pressure on North Korea over nuclear missiles, Mr Trump was the owner of the Miss Universe beauty pageant.

In 2013, Mr Trump took the pageant to Moscow and, to the surprise of many at a time when relations between the Obama administration and Moscow were strained, invited Mr Putin to attend.

Mr Trump in Moscow with Miss Universe 2013 Gabriela Isler and Russian businessman Aras Agalarov. ( Reuters: Maxim Shemetov )

Though it's still unclear whether the pair actually met in person or simply talked over the phone, the trip certainly seemed to have left a mark on Mr Trump.

"We just left Moscow. He could not have been nicer. He was so nice and so everything," Mr Trump said in a 2014 interview with Fox News' Eric Bolling.

According to Mr Trump, the Russian leader even sent him "a gift".

"I was in Moscow a couple of months ago … and they treated me so great. Putin even sent me a present," Mr Trump said in a speech at the Conservative Political Action Conference (C-Pac) in 2014.

"Beautiful present with a beautiful note."

'Trump is an absolute leader': Compliments galore ensue

Mr Trump has had an interesting relationship with Mr Putin. ( Reuters )

From there the friendship only seemed to flourish, with Mr Trump frequently claiming Mr Putin was a better leader than his own president Barack Obama, and from the moment Mr Trump announced his presidential campaign in June 2015, maintained that he would "get along very well with Putin".

"I think I get along with him fine. I think he would be absolutely fine," he told CNN's Anderson Cooper in July 2015 interview.

"He hates Obama. He doesn't respect Obama. Obama doesn't like him either, But he has no respect for Obama."

Mr Trump continued to shower praise on Mr Putin everywhere he went.

"Putin is a nicer person than I am," Mr Trump said at one New York press conference on September 28, 2015.

A day later on CBS, Mr Trump told Bill O'Reilly he would give Mr Putin an 'A' for his leadership.

Many Russian-Americans are confounded that Mr Trump is so benevolent toward their former country. ( Reuters: Sputnik/Mikhail Klimentyev/Kremlin )

But the compliments did not only flow one way, with Mr Putin praising Mr Trump's willingness to improve US-Russian relations.

"He is a very flamboyant man, very talented, no doubt about that," Mr Putin told reporters in December 2015.

"He is an absolute leader of the presidential race, as we see it today.

"He says that he wants to move to another level of relations, a deeper level of relations with Russia … how can we not welcome that?

"Of course, we welcome it."

The praise was not lost on Mr Trump, who responded in a statement that he was honoured "to be so nicely complimented by a man so highly respected within his own country and beyond".

And after his 2016 election victory, Mr Putin followed up by congratulating Mr Trump via telegram.

"We are ready to do our part and do everything to return Russian and American relations to a stable path of development," Mr Putin said.

'It's an honour to be with you': Meetings on the sidelines

Sorry, this video has expired Donald Trump and Vladimir Putin meet at the G20 summit in Hamburg last year.

Then, when the pair met for the first time as US and Russian leaders on the sidelines of the G20 summit in mid-2017 in Hamburg, the charm offensives from both sides were on full display.

"It's an honour to be with you," Mr Trump said. "Phone conversations are never enough definitely," Mr Putin said.

Rex Tillerson — then US Secretary of State — said the pair had immediate "positive chemistry" and were so engaged in conversation that they didn't want to stop.

A few months later in November, when the two leaders attended the APEC summit in Hanoi, they hit it off again.

So much so that despite the ongoing pressure on Mr Trump over the investigation into Russian interference in his 2016 presidential campaign, he said he "believed" Mr Putin "means it" when he said there was no Russian involvement in the election.

"He says he didn't meddle. I asked him again. You can only ask so many times," Mr Trump said.

"Every time he sees me, he said: 'I didn't do that.' And I believe, I really believe that when he tells me that he means it."

Sorry, this video has expired Trump: 'I believe he believes' Russia didn't meddle in election

'I don't know who Putin is': Trouble in Paradise

But the "relationship" hasn't all been so simple and clear-cut between Mr Trump and Mr Putin, with the two often backtracking that they know nothing about each other amid growing speculation Russia meddled in the Trump campaign.

"I never met Putin, I don't know who Putin is," Mr Trump said at a July 2016 news conference.

"He said one nice thing about me. He said I'm a genius. I said 'thank you very much' to the newspaper and that was the end of it. I never met Putin."

The backtracking sentiments were also echoed by Mr Putin, who claimed ahead of Mr Trump's inauguration he did not know Mr Trump and said people spreading lies about their relationship were "worse than prostitutes".

"I don't know Mr Trump. I have never met him and I don't know what he will do on the international arena," Mr Putin said.

"I have no reason whatsoever to assail him, criticise him for something, or defend him."

'We have a world to run': Trump wants Russia back in G7

Sorry, this video has expired A spokeswoman said Donald Trump's call to Vladimir Putin was protocol (Photo: Reuters)

Then more recently in April, Mr Trump contacted Mr Putin to congratulate him on his landslide election victory and hinted at holding their first official meeting, even as Moscow and Washington were clashing on two massive international issues — the crisis in Syria and the poisoning of former Russian spy Sergei Skripal and his daughter Yulia.

"I congratulated him on the victory, the electoral victory," Mr Trump told reporters at the White House while meeting Saudi Crown Prince Mohammed bin Salman.

"The call had to do also with the fact that we will probably get together in the not too distant future so we can discuss arms, we can discuss the arms race."

Mr Trump had Mr Putin's back at the G7 summit, calling on leaders to invite Russia back to the talks. ( Instagram: bundeskanzlerin )

The Skripal poisoning, which Britain quickly blamed on Russia, sparked Washington to expel 60 Russian diplomats. Moscow, in classic tit-for-tat diplomacy, ordered 60 US diplomats out of Russia.

Mr Trump did not directly weigh in on the strained ties, and when he congratulated Mr Putin by phone for his re-election but did not raise the spy case, it renewed questions about whether the US President sided too heavily with the Kremlin.

In early June this year at the G7 summit, Mr Trump branded himself as "Russia's Worst Nightmare" claiming that "Putin is probably going, 'man, I wish Hillary won'" while simultaneously calling for Russia to be reinstated into the G7 after it was suspended in 2014 following the annexation of Crimea.

"You know, whether you like it or not, and it may not be politically correct, but we have a world to run," he said.

"And in the G7, which used to be the G8, they threw Russia out, they should let Russia come back in, because we should have Russia at the negotiating table."

'Putin may be the easiest': Trump flies out to Europe

Sorry, this video has expired Donald Trump says meeting Putin will be easy

When the Helsinki summit meeting was arranged at the end of June, Mr Putin stressed the importance of a good relationship between the two nations, claiming he "has never been seeking confrontation" with the US.

And before setting off to Europe for the NATO summit, a United Kingdom visit, and the much anticipated US-Russia summit in Helsinki, Mr Trump was confident that meeting with his Russian counterpart would be "the easiest of them all".

"I have NATO, I have the UK, which is in somewhat turmoil, and I have Putin. Frankly, Putin may be the easiest of them all.

"Frankly, Putin may be the easiest of them all. Who would think? Who would think!" Mr Trump told reporters.

Then while in Brussels, just days before arriving in Finland, Mr Trump oddly launched a tirade against Chancellor Angela Merkel's Government claiming that a new energy pipeline would make Germany "totally controlled by" and "captive" to Russia.

"You tell me if that is appropriate because I think it's not," Mr Trump said, before slamming ally Berlin's failure to significantly increase NATO defence spending.

Now all eyes are on the Finnish capital and the 19th-century Presidential Palace that will play host to the summit.

Whether Mr Trump and Mr Putin emerge from their meeting singing mutual praise, giving each other the cold shoulder, or — as is often the case with these two unpredictable leaders — something else entirely, is yet to be seen.