For more infomation, see Humans.
Aliens is the term that the animals use to describe humans.
Personality
The Aliens are very nice to the penguins but they don't see it, Mumble was taken by an "Alien" but was brought back with some sort of traker on his back, he was fine with it, but his parents weren't. The Aliens seem to intereact with Mumble, they can reply back to Mumble, every time he dances by dancing back.
Looks
Despite the nickname the penguins have given, the aliens look like live-action humans.
Gallery
Aliens arriving.
Aliens dancing.
Aliens finding a way to get to Emperor-Land.
Aliens finding out that there is a snowstorm in Emperor-Land.