AVENTURA, Fla. — Cesar Sayoc Jr. was a volatile nobody desperate to become a somebody.

He styled himself as a bodybuilder, entrepreneur, member of the Seminole tribe and exotic-dance promoter in the status-hungry beachfront world of South Florida. In reality, Mr. Sayoc, a fervent supporter of President Trump who has been charged with mailing pipe bombs to prominent Democrats, was a bankrupt loner who spewed anger and spent years living in and out of a van, according to court documents and interviews with people who knew him.

He went on racist, anti-gay tirades at the Fort Lauderdale pizza shop where he worked as a night-shift deliveryman in 2017, telling his manager, a lesbian, that she and other gay people along with Democrats should all be put onto an island and then “nuked.” At a reunion event in 2015 with his college soccer team, he browbeat former team members with racist, sexist conspiracy theories.

And when Mr. Sayoc’s mother and sisters urged him to seek mental-health treatment, he furiously repelled their efforts and told his mother he hated her, said Ronald Lowy, a lawyer for the family who also represented Mr. Sayoc in a 2002 case in which he threatened to bomb an electric company during a dispute over a bill. He refused to even listen when his mother reminded Mr. Sayoc that he was Filipino and Italian, not Seminole, Mr. Lowy said.

“He had tremendous anger slowly boiling up, and resentment, and felt ‘less than,’” Mr. Lowy said. “He lacked an identity. He created a persona.”