U.S. President Barack Obama and Donald Trump met at the White House in a first attempt to turn their political rivalry into a smooth transfer of power.

In a meeting in the Oval Office on Thursday, President Obama said it鈥檚 time to unite.

鈥淚 believe that it is important for all of us, regardless of party and regardless of political preferences, to now come together, work together, to deal with the many challenges that we face.鈥�

He said to Trump, 鈥淲e now are going to, want to do everything we can to help you succeed, because if you succeed, the country succeeds.鈥�

President-elect Trump thanked Obama and said the meeting that was supposed to last ten minutes actually went on for an hour and a half.

He then told Obama, 鈥淚t was a great honour being with you and I look forward to being with you for many more times in the future.鈥�

Despite their cordial behaviour, it鈥檚 no secret the two men have a long history of bitter insults and public condemnation, even though the two had never met before this meeting.

Here鈥檚 a look at some of the most contentious moments between the outgoing President Obama and his successor Donald Trump.

Birther controversy

The bitter history between President Obama and Donald Trump dates back to 2011, when the 鈥渂irther鈥� controversy took root. Donald Trump relentlessly questioned whether President Obama was born in the United States. He also pushed for the president to release his birth certificate, an act which many have called 鈥渞acist.鈥�

Release of birth certificate

President Obama eventually released his birth certificate, which many say was the result of Donald Trump鈥檚 relentlessness. But Obama didn鈥檛 take the controversy sitting down. When he released his long-form birth certificate, he took a jab at the billionaire businessman saying, "We're not going to be able to solve our problems if we get distracted by sideshows and carnival barkers."

Still, Trump continued to question Obama鈥檚 nationality, most recently in January.

In an interview when he was asked if he believed President Obama was truly an American citizen, he said, "Who knows? Who cares right now? We're talking about something else, OK? I mean, I have my own theory on Obama. Someday I'll write a book."

But finally, this past September , "President Barack Obama was born in the United States, period." Still, he made no apology for the five years he claimed otherwise.

Contentious relationship ever since

Ever since the 鈥渂irther鈥� controversy gained steam, the two men have hurled insults at each other in the press. President Obama had some fun with the controversy stirred by Trump. He walked out to the song 鈥淩eal American鈥� by Rick Derringer and even showed a clip from 鈥淭he Lion King,鈥� saying it was from his 鈥渓ong-form鈥� birth video.

Obama also joked about what could happen if Trump ever made it to the White House, including a suggestion the real estate developer would turn it into a tacky casino.

Election season barbs

In August,

In response,Trump tweeted that "President Obama will go down as perhaps one of the worst presidents in the history of the United States!"

Release of controversial video

After the public release of a 2005 video in which Trump is heard talking about assaulting women,

While addressing Trump鈥檚 controversial candid comments she said, "I can't stop thinking about this. It has shaken to me to my core in a way that I couldn't have predicted.鈥� She went on to say the comments were indicative of Trump鈥檚 long history of disrespecting women.

Election promises

During the election, Donald Trump made it clear that, if he was elected, he would reverse many of President Obama鈥檚 policies, including Obamacare and the Trans-Pacific Partnership trade deal.

Social media weighs in on meeting

Given all the history between the two men, people were quick to comment about the Oval Office meeting on social media.