When Mike Johnson, the new House speaker, talks about race in America, he often draws a striking personal connection, telling the story of how he and his wife, Kelly, “took custody” of a Black teenager 24 years ago and raised him as a son.

“I have walked with him through discrimination that he has had to endure over the years and the hurdles he sometimes faced,” he told a House committee in 2019, while testifying against reparations for slavery. “I know all this because I was with him.”

When Mr. Johnson was named House speaker this week, his relationship with his son, like much of Mr. Johnson’s personal and political life, faced new scrutiny. There is no mention of the man, who is now an adult, raising his own family in California, in Mr. Johnson’s official biography. And he does not appear in the family photos posted on the congressman’s website. Mr. Johnson has four biological children: two daughters and two sons.

On Friday, Mr. Johnson sought to explain the absence, saying it was in deference to his son Michael’s request for privacy.

“At the time of the speaker’s election to Congress, Michael was an adult with a family of his own,” Corinne Day, the speaker’s communications director, said in a statement first reported by Newsweek. “He asked not to be involved in their new public life. The speaker has respected that sentiment throughout his career and maintains a close relationship with Michael to this day.”

The attention now being paid to Mr. Johnson — as well as to Michael — reflects the new world he has entered with his abrupt move to a position that puts him second in the line of succession to the presidency. Before this week, Mr. Johnson was an obscure southern Republican, with little known about his background beyond his home state; the story of Michael, who was 14 when he joined the Johnson family, was even less known.

In his public remarks over the years, Mr. Johnson describes Michael as his son and did not correct an interviewer who described Michael as “adopted.” Ms. Day said in an interview that the Johnsons did not formally adopt Michael because of the “lengthy adoption process.” Ms. Day declined to say whether Michael was using “Johnson” as his surname.

Michael could not be reached for comment.

Mr. Johnson has spoken publicly about Michael largely when he has talked about race. He has described Michael as a “success story” and likened the experience of being a white couple adopting a Black teenager to the movie “The Blind Side,” the 2009 film that depicts a wealthy white family taking in an impoverished Black teenager who becomes a football star.

In his testimony on racial reparations before a subcommittee of the Judiciary Committee, Mr. Johnson said that Michael, too, opposed reparations because it defied an “important tradition of self-reliance.” Mr. Johnson’s comments drews boos from supporters of reparations in the hearing.

Black lawmakers in Congress, who are overwhelmingly Democratic, did not welcome Mr. Johnson’s rise. The Congressional Black Caucus issued a statement this week upon Mr. Johnson’s election to the speakership describing him as “a Trump-backed extremist who wants to criminalize abortion and cut programs like Social Security and Medicare.”

Mr. Johnson’s remarks on race have also drawn criticism from the right. In a 2020 interview on PBS, he spoke with the journalist Walter Isaacson about racial tensions in America in the immediate aftermath of the killing of George Floyd, a Black man, by a white Minneapolis police officer. Mr. Johnson described the killing of Mr. Floyd as “an act of murder,” and said he had learned about racial disparities in America firsthand from raising a Black son.

At the time, Mr. Johnson noted that his oldest biological son, Jack, was now the same age as Michael was when he came into the house. “And I’ve thought often through all these ordeals over the last couple of weeks about the difference in the experiences between my two 14-year-old sons,” he said in the PBS interview. “Michael being a Black American and Jack being white Caucasian. They have different challenges. My son Jack has an easier path. He just does.”

When he was nominated for House speaker this month, Mr. Johnson — a hard-line conservative whose election to the new post has been applauded by the conservative movement — earned for those remarks rare criticism from the right, which viewed them as an acknowledgment of systemic racism.

Matt Walsh, a right-wing podcaster on The Daily Wire, wrote on X that Mr. Johnson’s comments about Mr. Floyd amounted to a “full fledged endorsement of the Left’s racial narrative” and called the 2020 interview “completely disqualifying.”

Laura Loomer, a far-right ally of Donald J. Trump, accused Mr. Johnson of being an “undercover Democrat,” asking in a post on X: “What type of MAGA Republican says something like this?”

But when asked about the criticism in his first lengthy interview since becoming speaker, Mr. Johnson appeared to downplay the role he believes race played in the lives of Jack and Michael.

“Having raised two 14-year-old boys in America and the state of Louisiana, they had different experiences,” he told the Fox News host Sean Hannity on Thursday. “And I’m not so sure it was all about skin color, but it is about culture and society. Michael, our first, came from a really troubled background and had a lot of challenges.”

Ken Bensinger contributed reporting.