With the aid of experts and clips, ABC threaded Mr. Jenner’s story with information about the transgender world, marking signs of acceptance (a Time Magazine cover and the award-winning Amazon series “Transparent”) and also the vestigial stigmas that lead some people to depression, isolation and even suicide. ABC provided profiles of Christine Jorgensen and the tennis player Renee Richards.

“I’m not stuck in anybody’s body, it’s just who I am as a human being,” Mr. Jenner said. “My brain is much more female than it is male.” And while he showed Ms. Sawyer a black cocktail dress he would wear to a private dinner the two had planned, he didn’t allow himself to be filmed in women’s clothes — and that was the right call. Mr. Jenner explained that his femininity isn’t located in his sexuality or appearance, but in his soul. There was no need to give paparazzi a tabloid shot of his new physique.

He rather sweetly said that for now, his aspirations for his newfound freedom are modest. He said he wanted to “be able to have my nail polish on long enough that it actually chips off.”

This was a coming-out about gender identity and also of television genre. Mr. Jenner tried to disentangle himself from his reality show skin, shedding the slightly goofy, Father Knows Least persona he plays on E! to reveal a more forceful and assertive version of himself. He became exercised – and even sarcastic — when Ms. Sawyer told him that his Kardashian years (she only referred to the series as “that reality show”) made people wonder whether this too was a publicity stunt. “Yeah, right,” he drawled.

Instead, he reframed his reality show career as the price he paid to create a platform for his new calling. “Yeah, I know,” he said, referring to what Ms. Sawyer described as “a shameless selling of everything.” He said this was different. “But what I am doing is going to do some good and we’re going to change the world. I really firmly believe that,” he said shaking his finger at Ms. Sawyer. He added, “And if the whole Kardashian show and reality television gave me that foothold into that world, to be able to go out there and really do something good, I’m all for it. I got no problem with that. Understand?”