Around Christmas, parents start hearing a lot about Elmo, the red, grinning, googley-eyed Muppet doll based on the Sesame Street character. The Elmo Doll has been a smash hit since it first hit shelves in 1996, topping "favorite toys" lists almost every Christmas.

There are a bunch of theories explaining why toddlers go seriously gaga for the doll. They find bold red comforting, for one. Also, he talks in familiar "mother-ese," and giggles when you poke its tummy — which is apparently a kind of cat nip for kids.

That all makes sense, but Robert A. Ferdman at Quartz points out another reason the doll flies off shelves: Tyco Toys keeps making new Elmos, and toy stores keep stocking their shelves with them. As Ferdman puts it, it's kind of a self-fulfilling prophecy.

[W]hile Elmo’s toy franchise is formidable, his popularity has as much to do with the risk-averse nature of retailers as it does with actual demand for furry red dolls. “Retailers only buy things that have proven to sell,” says Sean McGowan, senior analyst at Needham and Company. “And Elmo sells.” [Quartz]

This makes Elmo, as well as Barbie and other toys, a lot like successful film franchises. Both toy makers and studios make franchises out of products that resonate deeply with audiences, releasing new iterations every so often with slight adjustments.

For Elmo, it started with 1996's "Tickle Me Elmo" — a doll so insanely popular that parents were willing to steamroll store clerks to get their hands on one that Christmas season. The U.K's The Independent wrote this at the time:

The toy has captured the requisite rush of media attention. Whose pen-portrait graced the front page of the Wall Street Journal's Marketplace section yesterday? Tickle Me Elmo's. It is a serious commodity, after all, that is priced at $29 (pounds 18) but can be sold at over a grand.

A fresh story of Elmo-mania lands almost daily. At the weekend, an assistant in a Walmart superstore in Canada ended up in hospital after being trampled at 3 o'clock in the morning by some 300 frenzied parents attracted by a middle-of-the-night special Elmo sale. [The Independent]

Since then, the company has released a new Elmo just once a year, right around the holidays. Each one is slightly different from the last, with some nearly identical to earlier incarnations. There's a Let's Rock Elmo and a Rock n' Roll Elmo, for example. There are also two Tickle Me Elmos — the old one that laughs on one octave, and the 10th anniversary version that laughs a bit differently the second and third time you squeeze it.

Like the most successful franchises, such as James Bond for instance, there's something enduring about the character that makes people come back not just two or three times, but year after year after year. James Bond has masculine mystique. Elmo has toddler mystique. As Melinda Wenner Moyer explains in Slate, "We all love characters we can relate to."

Elmo is much like your little angel. I don’t mean to imply that your child is a muppet (although sometimes mine does resemble one); I mean that Elmo almost perfectly captures a toddler’s approach to and outlook on the world. [Slate]