United Auto Workers President Shawn Fain took the stage and began by thanking President Joe Biden for joining the picket lines during their strikes against the major auto companies last year.

Fain praised Vice President Kamala Harris for her years of supporting the UAW and for fighting for workers' rights.

"It's real simple. Kamala Harris is one of us. She's a fighter for the working class. And Donald Trump is a scab," Fain said to the crowd who chanted "Trump is a scab."

Fain revealed a shirt with that statement along with "Vote Harris" midway through his speech citing Nelly's 2002 song "Hot in Here."

"It's hot in here because you're fired up and you're fed up and the American working class is fired up and fed up," he said.

Fain also called out Trump's rhetoric blaming economic problems on several groups including immigrants and LGTBQ groups.

"Trump is pushing divide and conquer tactics of the rich. It's the oldest trick in the book," he said.

"They do that because they want working-class people to be divided into focus and keep the focus off the one true enemy: corporate greed. The rich think we're stupid, but working class Americans see this for what it is," Fain added.

Golden State Warriors coach Steve Kerr got a standing ovation when he walked on stage, just over a week after he coached the U.S. Olympic men's basketball team won gold.

Chants of "USA" stretched across the convention floor as he started speaking.

"It was the proudest moment of my life," he said, recounting the team's victory in Paris earlier this month.

Kerr called the audience to action -- asking the country to follow in the footsteps of the American basketball team's gold medal performance in Paris.

"After the results are tallied [on election] night, we can, in the words of the great Steph Curry, we can tell Donald Trump, 'night-night.'"

Convention staff is preparing for possible disruptions over Gaza during President Joe Biden's keynote speech.

ABC News has heard from staff and activists that they likely won't come from uncommitted delegates on the convention floor, but are expected to come from activists who have passes into the arena who are in sections higher up.

-ABC News' MaryAlice Parks and Isabella Murray

Actor Tony Goldwyn, who famously played a president on TV in ABC's "Scandal," has arrived for the primetime hour of the DNC's first night.

Goldwyn said the choice between Harris and Trump is between "two very different futures" for our middle class, reproductive rights, climate, security, schools and "the future of our very democracy."

He said Harris has a message for America.

"It is a message that's joyful, not mean-spirited, a message of public service, not self-service, a message of optimism and opportunity, not chaos and division. A message that has woken us up to who we are, to who we've always," he said.