But FX Networks, whose FXX carries “The League,” said that while Mr. Rannazzi’s deception had been “upsetting” and “unfortunate,” it still would go forward with him as a character in the show’s final season. It has produced 11 of the 13 episodes, and production of the final two is not expected to be completed until mid-October. “We believe Steve is sincere in his apology and will do everything he can to make amends moving forward,” the network said in a statement.

Mr. Rannazzisi, who declined requests for an interview, said in his statement that once he had lied, he could not figure out a way to undo the damage.

“For many years, more than anything,” he said, “I have wished that, with silence, I could somehow erase a story told by an immature young man. It only made me more ashamed. How could I tell my children to be honest when I hadn’t come clean about this?”

His interviews, though, several of which remain posted on the Internet, show that a decade after the Sept. 11 attacks, Mr. Rannazzisi was still relating a harrowing experience. In a 2011 interview on the podcast “Sklarbro Country,” Mr. Rannazzisi said that he had gotten a good severance package from Merrill Lynch and that he clearly understood that Sept. 11 was a sensitive topic. “I’ve spoken about it before,” he said. “I just don’t ever want to feel like, anyone, I am cashing in or anything like that.”

Mr. Rannazzisi, who is originally from Long Island, is far from the first person whose Sept. 11 account has been exaggerated or, as is the case here, false. The most startling example was a Spanish woman, Alicia Esteve Head, who went by the name Tania Head. She joined the World Trade Center Survivors’ Network support group and went on to become its president, but her story of escape from the 78th floor of the south tower was fabricated. She was believed to be in Barcelona, Spain, on Sept. 11.

Her rationale for suggesting she was there remains no clearer than Mr. Rannazzisi’s. But what is clear is that, since he moved to Los Angeles shortly after the attacks, with his girlfriend, now his wife, his profile has risen steadily. In 2003, he was noticed by the actor Ashton Kutcher, who gave him his first TV role, as a cast member on MTV’s “Punk’d,” according to Mr. Rannazzisi’s website.