Big Papi is on the Wu train.

Boston Red Sox legend and Hall of Famer David Ortiz is backing Michelle Wu for mayor, the Wu campaign announced Thursday.

“Boston has always been special to me, and I care deeply about its future,” Ortiz said in a statement. “I’ve gotten to know Mayor Wu and I’m impressed by her dedication to bringing people together across our neighborhoods.

“That’s why I’m proud to support Mayor Wu — because Boston deserves someone who shows up for all of us.”

Ortiz, 49, was part of three World Series championships with the Red Sox and was inducted into the Baseball Hall of Fame in 2022. He works as an MLB studio analyst for FOX Sports, and lives in Florida, according to his FOX network biography.

Wu, who is seeking a second term, said she was “honored” by the endorsement.

“To have the support of Red Sox legend David Ortiz means the world to me — not just as a fan, but as someone who believes deeply in the spirit of Boston,” Wu said in a statement. “Big Papi has always represented the heart of our community and I’m honored by his endorsement.

“This is our city — and together, we’ll keep making Boston a home for everyone.”

Wu, 40, is facing a challenge from Josh Kraft, a son of the billionaire New England Patriots owner Robert Kraft and longtime philanthropist; community activist Domingos DaRosa and City Hall employee Kerry Augustin.

As of Thursday, eight other candidates had filed paperwork to run for mayor.

Wu’s campaign said Wednesday that it had turned in 3,500 signatures on the first day of signature collection. Kraft’s campaign countered Thursday by saying that it had collected 6,500 signatures on the first day.

Mayoral candidates need to submit 3,000 signatures to appear on the fall ballot.