Barack Obama has made his return to the public eye with a wry reference to his White House successor, but avoided speaking the name Donald Trump as he laid out his plans for life after the presidency.

The panel at the University of Chicago was the 55-year-old former Democratic president's first public engagement since leaving office.

"So, uh, what's been going on while I've been gone?" he joked, barely suppressing a smile as laughter broke out in the audience.

It comes after a lengthy post-presidential holiday that saw the two-term president kitesurf with Richard Branson in the British Virgin Isles and take multiple vacations, including to the South Pacific Island of Tetiaroa, once owned by Marlon Brando.

The former president didn't mention his successor, Donald Trump. ( AP: Charles Rex Arbogast )

Mr Obama, who once taught constitutional law at the University of Chicago, recalled starting out as a young community organiser in the city as he addressed an audience of hundreds gathered to hear him speak.

He told a panel of six current and former students that he decided to focus his future efforts on encouraging young people to engage with their communities.

"The single most important thing I can do is to help in any way prepare the next generation of leadership to take up the baton and to take their own crack at changing the world."

The elephant in the room: Donald Trump

Mr Obama has largely stayed out of the public eye since leaving office in January, despite efforts by Mr Trump and the Republican-led Congress to undo much of his legacy, including on health care and the environment.

Mr Trump, a Republican, has said he "inherited a mess" and accused Mr Obama in March, without providing evidence, of wiretapping his 2016 presidential campaign.

Barack Obama looked relaxed as he returned to the public stage in Chicago. ( AP: Charles Rex Arbogast )

Mr Obama has denied the charge and FBI director James Comey told a congressional hearing he had seen no evidence to support the allegation.

Mr Obama was not asked about Mr Trump by the students and he took no questions from reporters.

Saying it had long been his goal to bridge the country's deep political divide, Mr Obama said:

"It's harder and harder to find common ground because of the money in politics. Special interests dominate the debates in Washington in ways that don't match up with what the broad majority of Americans feel," he said.

Mr Obama added that changes in the way people used media allowed them to converse just with those who agreed with their own points of view.

On Sunday, as part of a program to help at-risk young people, Mr Obama met privately with men from Chicago's troubled south side to discuss solutions for the violence and joblessness that have marked that neighbourhood.

The former president, who together with his wife Michelle recently struck a two-book, $65-million memoir deal, is expected to travel to Berlin to meet with German Chancellor Angela Merkel next month.

Wires/ABC

