The alien invaders in the 2014 film "Edge of Tomorrow" are called Mimics.
The Mimics have occupied much of continental Europe when Major William Cage, played by Tom Cruise, is forced into combat despite having no battlefield experience. During the disastrous landing operation, Cage gains the ability to relive the same day whenever he dies, giving humanity a chance to learn how the alien army operates.
The name "Mimics" reflects the creatures’ ability to anticipate and counter human military tactics. They are not all identical: Alpha Mimics act as powerful commanders, while the Omega is the central organism coordinating the invasion. This hierarchy is important to the plot because defeating the Omega can change the course of the war.
The film was adapted from Hiroshi Sakurazaka’s 2004 Japanese light novel, published in English as "All You Need Is Kill." A common mix-up is confusing the Mimics with the Alpha or Omega; those are specific types within the larger alien species.