Former President Barack Obama will return to the Democratic National Convention stage in his hometown of Chicago to deliver the keynote address on Tuesday, 20 years after his convention debut thrust him into the national spotlight.

It’s a tricky moment for one of the party’s most popular figures.

He will use his speech to touch on the historic nature of Kamala Harris’s candidacy – the first female of colour to lead the ticket – as a continuation of his legacy. But he must also pay tribute to his own vice-president and the man responsible for her rise – President Joe Biden.

Mr Obama, 63, and Ms Harris, 59, have moved in overlapping political orbits as early as his days as an Illinois state senator running for the US Senate. The two, both on the rise in their nascent political careers, met at a California fundraiser in 2004.

As an early supporter, Ms Harris would later volunteer for his presidential campaign and help power his first victory in 2008. Buoyed by party enthusiasm for Ms Harris’s campaign, Mr Obama – and his popular wife Michelle Obama – will try to return the favour and help propel her to the Oval Office.

“I think he can excite people about her and about the stakes [of the election] and I think that’s what he intends to do today,” David Plouffe, Mr Obama’s 2008 campaign manager and a now Harris campaign adviser, told Axios.

Here’s a look at key moments in their two-decade relationship.

Ms Harris, then a San Francisco district attorney, was in the crowd of more than 15,000 people as then-junior senator announced his longshot bid for the White House on the steps of the Old State Capitol in the Illinois capital city of Springfield in February 2007. She would go on to knock on doors and raise money for Mr Obama ahead of the Iowa caucuses in 2008, later serving as his California campaign co-chair.

Mr Obama lent her some of his national star power two years later when she mounted a statewide bid for attorney general against Republican Steve Cooley, a popular Los Angeles district attorney. She had been affectionately referred to as “the female Barack Obama” by longtime PBS News anchor Gwen Ifill, but remained locked in a tight contest.

Mr Obama, who would endure widespread congressional losses in that election year, made time to appear at a Los Angeles rally in October 2010 in which he referred to Ms Harris as “dear, dear friend of mine”.

“I want everybody to do right by her,” he told the crowd. Ms Harris eked out a victory by less than a percentage point, setting her on a path toward higher office.

Mr Obama gave Ms Harris a coveted speaking role at the 2012 Democratic National Convention for his re-election.

She had already made a name for herself in California in barrier-breaking roles as the first person of colour or woman to serve as San Francisco’s district attorney. She was also the first African American and South Asian American elected as the state’s top lawyer.

But as attorney general, she had made headlines for standing firm in negotiations on a financial settlement between state attorneys general and the banks responsible for the foreclosure crisis, securing more than $25 billion on behalf of homeowners.

She spoke of her accomplishment, weaving in her personal story, praising Mr Obama for standing up for Americans during the housing crisis and attacking his Republican challenger Mitt Romney as an ally of Wall Street.

“We need to move forward.” she said in her speech, a phrase she has reprised in her 2024 campaign. “President Obama will fight for working families. He will fight to level the economic playing field and fight to give every American the same fair shot my family had.”

Her high-profile remarks came just before former President Bill Clinton, landing a spot that was guaranteed to catch the attention of national Democrats, powerbrokers and key donors.

Though Mr Obama quietly supported Ms Harris as she rose through California politics, he raised eyebrows in 2013 when he referred to her as “the best looking attorney general in the country”.

“You have to be careful to, first of all, say she is brilliant and she is dedicated and she is tough, and she is exactly what you’d want in anybody who is administering the law, and making sure that everybody is getting a fair shake,” the president said at a San Francisco fundraiser. “She also happens to be, by far, the best looking attorney general in the country.”

He phoned Ms Harris hours later to apologise for the comment.

“They are old friends and good friends and he did not want in any way to diminish” her accomplishments, White House spokesman Jay Carney later told reporters.

At the height of his Democratic power in 2016, finishing his second term as president, Mr Obama waded into the contentious California Senate race to endorse Ms Harris, who launched a bid to replace retiring Senator Barbara Boxer.

In July of that year, he and Vice-President Joe Biden formally announced their support for Ms Harris, who was running against fellow Democrat and US Congresswoman Loretta Sanchez. In California’s primary system, the two top vote-getters advance to the general election, regardless of party.

“Kamala is a lifelong courtroom prosecutor with only one client: the people of the State of California. That’s the approach she’ll take to the United States Senate,” Mr Obama said in a statement released by the Harris campaign.

Mr Biden said he had known her through his son Beau Biden, who forged a friendship with Ms Harris as Delaware’s attorney general during their mortgage settlement negotiations.

Ms Harris handily won the election, and became only the second black female to serve in the US Senate.

Ms Harris’ 2020 presidential primary bid began as a spectacle, launched in her hometown of Oakland, California, before a crowd of 20,000 people in 2019. Like others in the crowded field of candidates vying for the Democratic nomination, she met with Mr Obama to lay out her case for her candidacy.

But Mr Obama, whose own vice-president was mounting an election bid, wanted to stay out of the political fray and wait until the party selected its nominee before offering his coveted endorsement.

Ms Harris’s campaign collapsed in less than a year, and Joe Biden would offer her a political reprieve as his running mate. Mr Obama reportedly supported Mr Biden’s selection of Ms Harris, despite their early debate clash over the former vice-president’s record on school desegregation.

Mr Obama said his former vice-president “nailed this decision” in selecting Ms Harris.

“Choosing a vice-president is the first important decision a president makes. When you’re in the Oval Office, weighing the toughest issues, and the choice you make will affect the lives and livelihoods of the entire country — you need someone with you who’s got the judgement and the character to make the right call,” Mr Obama said in a statement at the time.

Since 2020, Mr Obama has been in regular touch with Ms Harris, providing counsel and serving as a sounding board whenever she’s asked.

The Obamas waited several days to endorse Ms Harris until it was clear that there were no challengers and she was the party’s choice. The couple released a video of them calling her to formally announce their support for her campaign.

“We’ve known each other for 20 years. I’ve watched how you have excelled in every position you’ve been in,” Mr Obama told her in the phone call. “Just to see all that hard work be recognised is something that we couldn’t be more thrilled about. And so the main thing we wanted to do was just let you know and let Doug [Emhoff] know, our soon-to-be first gentleman, that we are gonna do everything we can to help propel you into the presidency.”

Over the last few months, the two have been in close contact as Mr Obama has sought to offer support for her campaign, including policy or strategic advice, fundraising and get-out-the-vote efforts.

Ms Harris has also relied on many of Mr Obama’s old hands to help run her campaign. Eric Holder, who served as Mr Obama’s attorney general, led efforts to vet Ms Harris’s shortlist for vice-president, while Mr Plouffe is now serving as one of her most senior advisers.

The Harris campaign has also enlisted other Obama aides including Jennifer O’Malley Dillion, her campaign chairwoman, and senior adviser Stephanie Cutter. Former Obama communications director Jennifer Palmieri is also helping Ms Harris’s husband, Doug Emhoff.