The Aliens are the main antagonists of the 1996 film "Independance Day".
The Aliens are a large race of sapient, spacefaring creatures which travel from planet to planet destroying all life before moving on like a plague of locusts.
They are actually physically weak but have advanced technology which helps them become stronger and more durable.
They travel around the galaxy in a single, massive Mothership that is around 550km in diameter. They also have a large fleet of smaller ships used as fighters. Their ships are protected by a force field.
One ship crash landed in Roswell in 1947 and was taken to Area 51.
In 1996, they launched an attack on Earth, positioning their ships at major cities they almost destroyed all of mankind. However on the 4th of July, they were defeated and possibly driven to extinction thanks to the creation of a computer virus which temporarily removed the alien ships' shields, followed by a devastating nuclear attack on their orbiting mothership.