Puckmarin

The Puckmarin is a little alien character who befriends David Freeman in Flight of the Navigator. Puckmarins are from the planet Binpuka Minor, which was destroyed by a comet. Max managed to save the last surviving member of its kind, but found he could not return it to it's home planet.

At the end of the movie, the little Puckmarin stows away in David's backpack.