Missing Richard Simmons topped the iTunes chart within two weeks of launching and it’s not difficult to see why. This is the compelling true story of a man who built an empire, became the butt of a thousand jokes, then turned his back on the world at large. This podcast is like Serial with spandex.

For the uninitiated, Richard Simmons made his name in the 1980s as the pint-sized fitness trainer with the shock of curly hair, screeching voice and inclusive attitude towards exercise. Like “Weird Al” Yankovic, his eccentricity made him an easy target for gags, but his countless talk show appearances and bon mots such as “sweat is just fat crying” suggest a man in on the joke. More crucially, America took to the man and his fitness tapes; Simmons is thought to be worth somewhere in the region of $15m (£12m).

The stories told on the podcast about Simmons’ kindness are staggering. One interviewee mentions bumping into the fitness guru during a period when she was morbidly obese and feeling suicidal. Simmons made a point of introducing himself, making conversation and exchanging numbers. He proceeded to call this stranger at least once a week for a period of years just to see how she was getting on. This was unpaid work, simply the behaviour of a Good Samaritan, and the recipient credits Simmons with saving her life. She is not the only one.

One of the last public photos taken of Simmons at a Hurricane Sandy benefit (Getty)

An intensely private person, Simmons nonetheless made sure that those on bus tours were treated to an experience they’d never forget. While most Hollywood celebrities positively despise the very concept of such tours, he was noted for coming down and greeting visiting tourists while patiently posing for photographs. This even extended to the time a car ran over his foot and, despite evident discomfort and loss of blood, he continued to schmooze his adoring public. While this might sound apocryphal, the video on YouTube confirms it is anything but.

Missing Richard Simmons is the work of Dan Taberski, a man with little interest in exercise until he joined the class run by the titular trainer in California for the last 40 years. The pair became firm friends and it is worth noting that Simmons started the class before he made his fortune and continued long after becoming a multimillionaire, notoriously almost never missing a session. That is until February 2014, when he failed to show up. He’s not been heard from since and Taberski wants to know how a man so full of life could just turn his back on his own.

Some have suggested that if Simmons wishes to be alone then he should be permitted to live out his Garbo-esque fantasy in peace, and yet the appeal of the podcast lies in the mystery at its core. This was a man who seemed to revel in human interaction above all else, so to vanish without a word seems entirely out of character – not least because his friends would be content to receive just a one-line email if it really is that simple. One can’t help but feel sorry for the nonagenarian lady interviewed who counts Richard as a close friend and cannot make sense of the fact that he’s severed all ties.

She is just one of many friends and acquaintances interviewed as we slowly get a glimpse of the man behind the punchline. Conspiracy theories include kidnapping and the idea that Simmons is now living his life as a woman. Is it possible that his housekeeper is keeping him hostage? One close friend is adamant not only of this fact but also that the lady in question is an actual witch. What is the truth and might it just prove stranger than fiction? Taberski goes to great lengths, stake-outs et al, in a bid to track down the man at the centre of the mystery in the hope of getting him to agree to a chat.

The host’s aim is not to bring his friend back against his will but simply to find out why a man noted for his joie de vivre would become such a reclusive figure. Indeed, the first episode ends with an appeal for information that concludes with the words:

“If you’re listening to this and you’re actually Richard Simmons, call me. People are looking for you.”