David Crowley, the Milwaukee County executive and a moderate Democrat, won the Democratic nomination for governor of Wisconsin early Wednesday, upsetting a democratic socialist who had held a significant lead in opinion polls.

Mr. Crowley had dropped out of the race last month, only to jump right back in and score an endorsement from Gov. Tony Evers after another leading candidate ended her campaign. But because of the energy that Francesca Hong, the democratic socialist candidate, was generating from a motivated progressive base, Mr. Crowley received far less attention in the race.

Here are five things to know about him:

1. He trailed far behind in limited opinion polls of the primary race. Mr. Crowley had been seen as a long-shot candidate going into Tuesday, with Ms. Hong widely seen as the front-runner.

But her position also attracted some challenging headlines over past comments she had made criticizing holidays including Thanksgiving and Halloween. Prominent progressives including Representative Alexandria Ocasio-Cortez of New York and Senator Bernie Sanders of Vermont declined to endorse her. And many Democrats fretted that she would not be a competitive general-election candidate in a battleground state.

Mr. Crowley, meanwhile, tried to capitalize on Ms. Hong’s struggles, casting himself in the final days of the race as a choice with bipartisan appeal.

2. He was endorsed by Mr. Evers. Mr. Crowley found an important late-race champion in the departing Democratic governor, whose decision not to run for a third term set the stage for the contest. Mr. Evers argued that Mr. Crowley would be a strong general-election candidate and that his background leading Wisconsin’s largest county would prepare him for the job of governor.

“He gets stuff done,” Mr. Evers said at one event, adding: “He is an administrator. He is an executive. And he’s got a heart as big as they come.”

3. He would be Wisconsin’s first Black governor. Mr. Crowley has already broken some barriers in Wisconsin. He is the first Black Milwaukee County executive. Now 40, he also became the youngest person to serve in the role when he took the post six years ago.

4. He has said he was evicted from homes three times as a child. Mr. Crowley, who grew up on Milwaukee’s North Side, has leaned into his personal history. Both of his parents struggled with addiction and mental health challenges, according to his campaign. He has said his childhood inspired him to become a community organizer and later a state lawmaker. Even as a child, his family nicknamed him Governor, he has said.

“I wanted to feed my aunt, my grandmother, my uncles, take out the garbage and do the dishes,” he told The Capital Times of Madison. “I wanted to serve my family before I actually sat down and started eating. And so they used to call me ‘Governor.’”

5. He is cautious about proposing tax increases. Mr. Crowley has positioned himself as a moderate on taxes, expressing concern about raising them on the wealthy and calling for a “holistic” review of the tax system.

“We absolutely need to tax the ultrawealthy,” he said at a candidates’ debate last month. “But we need to be smart about how we’re doing things long-term.” And in a post on social media last month about property taxes, he wrote, “The taxes are too damn high.”