Former US President Barack Obama received a rock-star welcome in Berlin as he appeared at a public debate today with German Chancellor Angela Merkel, whom he praised as one of his favorite partners during his presidency. <br/><br/>Security was tight in front of the German capital's iconic Brandenburg Gate, where Obama and Merkel appeared on a podium before thousands of people attending a gathering marking the 500th anniversary of the Protestant Reformation. <br/><br/>After lauding Merkel as someone who had done outstanding work, Obama launched a defense of his own presidency and the values of liberal democracy championed by both leaders. <br/><br/>In a veiled reference to his successor Donald Trump, Obama also spoke of the need to see development aid and diplomacy as essential aspects of national security policy.<br/><br/>Merkel is due to travel to Brussels later today for a meeting with leaders of fellow NATO member states, including President Trump.