D'Artagnan (or Dart for short) was a Demogorgon from the Upside Down, found by Dustin Henderson in Stranger Things.
It was discovered on Halloween night by Dustin Henderson after he fond the creature in his trash can that keeps as a pet and feed it nothing but chocolate, he soon decided call it, D'Artagnan after a candy bar. Dart starts off as a tadpole-like creature that soon grow second pairs of legs, it has a mark on the top of it's bottom. Although carnivore, Dart liked eating candy that Dustin give it.
Once in stage three, Dart kills Dustin's pet cat; Mews, he locks it in the fallout shelter however it escape into the forest after change again and dig its way out. The children began looking for Dart only to found out that it wasn't alone as there more Demogorgons.
Dart was not seen again until the finale, where it encounters the kids but Dustin who knew Dart the best, feed it more chocolate bar before saying goodbye his dear friend. After Eleven closes the gateway, all the "Demodogs" immediately died of include D'Artagnan itself too.