Ultron is an android created by Hank Pym. Ultron grew a hatred for his creator, and ended up becoming one of his greatest villains, as well as the Avengers. He is also noted for creating Vision, and Jocasta, who both betrayed him, and became Avengers.
Ultron's body is comprised of adamantium, the strongest metal in the Marvel Universe. He also had displayed the ability to shoot beams of energy, and has been able to create other bodies, or copies of himself, sometimes in mass quantity.