Four or five times a week these days, some old friend will contact Louis Theroux and tell him, “My daughter keeps going around the house singing your rap,” or, “My wife was exercising to your rap in her Pilates class.” Passing by a primary school, Mr. Theroux has the feeling he is being watched, a sense confirmed when he hears a kid call out behind him: “My money don’t jiggle jiggle.”

His agent has been fielding dozens of requests for personal appearances and invitations to perform. Mr. Theroux, a 52-year-old British American documentary filmmaker with a bookish, somewhat anxious demeanor, has turned them all down, not least because, as he put it in a video interview from his London home, “I am not trying to make it as a rapper.”

But in a way, he already has: Mr. Theroux is the man behind “Jiggle Jiggle,” a sensation on TikTok and YouTube, where it has been streamed hundreds of millions of times. He delivers the rap in an understated voice that bears traces of his Oxford education, giving an amusing lilt to the lines “My money don’t jiggle jiggle, it folds/I’d like to see you wiggle, wiggle, for sure.”

For Mr. Theroux, a son of the American author Paul Theroux and a cousin of the actor Justin Theroux, the whole episode has been odd and a little unsettling. “I’m pleased that people are enjoying the rap,” he said. “At the same time, there’s a part of me that has a degree of mixed feelings. It’s a bittersweet thing to experience a breakthrough moment of virality through something that, on the face of it, seems so disposable and so out of keeping with what it is that I actually do in my work. But there we are.”

The story of how this middle-aged father of three has taken hold of youth culture with a novelty rap is “a baffling 21st century example of just the weirdness of the world that we live in,” Mr. Theroux said.

“Jiggle Jiggle” gestated for years before it became all the rage. It started in 2000, when Mr. Theroux was hosting “Louis Theroux’s Weird Weekends,” a BBC Two series in which he delved into various subcultures. For an episode in the third and final season, he traveled to the American South, where he met a number of rappers, including Master P. As part of the show, he decided to do a rap himself, but he had only a few meager lines: “Jiggle Jiggle/I love it when you wiggle/It makes me want to dribble/Fancy a fiddle?”

He enlisted Reese & Bigalow, a rap duo in Jackson, Miss., to help him work it into shape. Bigalow cleaned up the opening lines and linked the word “jiggle” with the word “jingle” to suggest the sound of coins in your pocket. Reese asked him what kind of car he drove. His reply — Fiat Tipo — led to the lines, “Riding in my Fiat/You really have to see it/Six-feet-two in a compact/No slack but luckily the seats go back.”

“Reese & Bigalow infused the rap with a genuine quality,” Mr. Theroux said. “The elements that make it special, I could never have written on my own. At the risk of overanalyzing it, the genius part of it, in my mind, was saying, ‘My money don’t jiggle jiggle, it folds.’ There was something very satisfying about the cadence of those words.”

He filmed himself performing the song live on the New Orleans hip-hop station Q93, and BBC viewers witnessed his rap debut when the episode aired in the fall of 2000. That might have been the end of “Jiggle Jiggle” — but “Louis Theroux’s Weird Weekends” got new life in 2016, when Netflix licensed the show and started streaming it on Netflix UK. The rap episode became a favorite, and whenever Mr. Theroux made the publicity rounds for a new project, interviewers would inevitably ask him about his hip-hop foray.

In February of this year, while promoting a new show, “Louis Theroux’s Forbidden America,” Mr. Theroux sat down for an interview on the popular web talk show “Chicken Shop Date,” hosted by the London comedian Amelia Dimoldenberg.

“Can you remember any of the rap that you did?” Ms. Dimoldenberg asked, prompting Mr. Theroux to launch into his rhymes in what he described as “my slightly po-faced and dry English delivery.”

“What happened subsequently is the most mystifying part,” he added.

Luke Conibear and Isaac McKelvey, a pair of DJ-producers in Manchester, England, known as Duke & Jones, plucked the audio from “Chicken Shop Date” and set it to a backing track with an easygoing beat. Then they uploaded the song to their YouTube account, where it has 12 million views and counting.

But “Jiggle Jiggle” became a phenomenon thanks largely to Jess Qualter and Brooke Blewitt, 21-year-old graduates of Laine Theater Arts, a performing arts college in Surrey, England. In April, the two friends were making pasta at their shared apartment when they heard the song and hastily choreographed moves suited to the track — dribbling a basketball, turning a steering wheel — and the “Jiggle Jiggle” dance was born.

Wearing hooded sweatshirts and shades (an outfit chosen because they weren’t wearing makeup, the women said in an interview), Ms. Qualter and Ms. Blewitt made a 27-second video of themselves performing the routine. It blew up shortly after Ms. Qualter posted it on TikTok. Copycat videos soon sprang up from TikTok users around the world.

“This was all going on without me knowing about it,” Mr. Theroux said. “I got an email: ‘Hey, a remix of the rap you did on “Chicken Shop Date” is going viral and doing extraordinary things on TikTok.’ I’m, like, ‘Well, that’s funny and weird.’”

It bursted out of TikTok and into the mainstream last month, when Shakira performed the “Jiggle Jiggle” dance on NBC’s “The Tonight Show Starring Jimmy Fallon.” Snoop Dogg, Megan Thee Stallion and Rita Ora have all posted themselves dancing to it. The cast of Downton Abbey jiggle-jiggled during a red carpet event.

“Anthony Hopkins has just done a thing yesterday,” Mr. Theroux said. “It would be too much to call it a dance. It’s more of a twitch. But he’s doing something.”

The whole episode has been strange for his three children, especially his 14-year-old son, who is big into TikTok. “‘Why is my dad, the most cringe guy in the universe, everywhere on TikTok?’” Mr. Theroux said, giving voice to his son’s reaction.

“I’ve left my stank all over his timeline,” he continued. “I think it’s made him very confused and slightly resentful.”

Ms. Qualter and Ms. Blewitt find it equally surreal to see Shakira and others dancing to their moves. “I almost forget that we made that up,” Ms. Qualter said. “It doesn’t feel like it’s happened. It’s got over 60 million views. We see the number on the screen, but I can’t comprehend that there are people behind it.”

After the original Duke & Jones remix went viral — that is, the one with the vocal track taken from “Chicken Shop Date” — the DJ-producer duo asked Mr. Theroux to redo his vocal in a recording studio. That way, instead of being just another TikTok ear-worm, “Jiggle Jiggle” could be made available on Spotify, iTunes and other platforms, and its makers could gain some exposure and profit from it.

In addition to Mr. Theroux, five composers are credited on the official release: Duke & Jones; Reese & Bigalow; and the 81-year-old hitmaker Neil Diamond. Mr. Diamond became part of the crew when his representatives signed off on “Jiggle Jiggle,” which echoes his 1967 song “Red Red Wine” in the part where Mr. Theroux’s Auto-tuned voice sings the words “red, red wine.” The song hit the Spotify viral charts globally last month.

So does this mean real money?

“I sincerely hope we can all make some jiggle jiggle out of the phenomenon. Or maybe some fold,” Mr. Theroux said. “So far, it’s been more on the jiggle end.”

In his career as a documentary filmmaker, Mr. Theroux has explored the worlds of male porn stars, the Church of Scientology, right-wing militia groups, and opioid addicts. In his new BBC series, “Forbidden America,” Mr. Theroux examines the effects of social media on the entertainment industry and politics. Years before Netflix had a hit show centered on Joseph Maldonado-Passage, who is better known as the Tiger King, Mr. Theroux made a film about him. The American documentarian John Wilson, the creator and star of HBO’s “How To With John Wilson,” has cited him as an influence.

Now his body of work has been eclipsed, at least temporarily, by “Jiggle Jiggle.” And like many who go viral, Mr. Theroux finds himself trying to understand what just happened and figure out what he’s supposed to do with this newfound cultural capital.

“It’s not like I have a catalog and, like, now I can release all of my other novelty rap fragments,” he said. “I’m clearly not going to tour it. ‘Come see Mr. Jiggle himself.’ It would be a 20-second-long gig.”