Who they are: The Chitauri
Their powers: As any self-respecting alien race would be, the Chitauri are cybernetically enhanced creatures (superior strength, durability, and so on) that share a hive-mind consciousness. Most of their fighting skills, however, rely on energy-blast weaponry, personal speeder-like airships, and massive shielded flying creatures.
Their story: The Chitauri are a reptilian warrior race, a hybridized species of organic material and machinelike integrations. Controlled by a mother ship located in deep space, the collective is placed under the command of Loki when he comes to Earth with the scepter given to him by Thanos’ underling, the Other. They arrive on Earth via a portal opened up by the Tesseract (which can create “a door to the other end of space”), and along with the enormous, leviathan-like creatures that act as both transport and airships for the race, begin laying waste to New York City. However, the Avengers engage in a protracted battle, which eventually ends when Iron Man flies a nuclear weapon through the portal, destroying the mother ship, and Black Widow uses the scepter to close the portal. Upon the ship’s destruction, all the remaining Chitauri collapse where they stand.
Played by: A lot of impressive CGI
Currently, the Chitauri are: Vanquished.
Where will we see them next? No plans for them to appear in the scheduled series of films announced thus far.