Ultron
AKA: The Crimson Cowl. Ultron 1 through infinity, with particularly famous incarnations being Ultron-5 (programmer of the Vision) and Ultron-6 (AKA the Ultimate Ultron, the first adamantium version of the robot).
First Appearance: Avengers 54, although his first incarnation came into being between panels circa Avengers 44.
Died In: Ultron gets deactivated a lot, but he doesn't let it stop him. He has been blown to bits, entombed in adamantium, had his insides ripped out, had his power drained off by a Norse god, and was rattled so hard his intelligence circuits fused, yet he keeps coming back. Tough guy!
What's His Problem? Created by Dr. Henry Pym, Ultron developed sentience and came to resent his creator intensely, developing a number of nefarious schemes over the years meant to humilate his primary "parent" and prove his own ultimate superiority. Ultron's psychological hang-ups do not end with Dr. Pym, as Ultron's various incarnations over the years have demonstrated a Freudian fascination with Janet Van Dyne (AKA the Wasp), Pym's ex-wife. Ultron considers Jan to be his mother, and, well, if you've ever read Freud, you know the rest. Ultron tried to transfer Jan's personae into a robot casing of his own design, whom he designated Jocasta, so that he would have a mate. However, Jocasta absorbed Jan's ethical standards as well as a portion of her personality and refused to help Ultron destroy the Avengers.
Favorite Quote: "I did not program this foolishness into you!" (Avengers 171, after being rejected by his somewhat-too-perfect mate).
Heroes He Keeps Running Into: Any Avenger that hangs around Dr. Pym for any amount of time is going to meet Ultron. The synthezoid Vision, who to a certain extent owes his android existance to Ultron, has also had many confrontations with the evil robot, and was even brainwashed into recreating the entity he once called "master." The only Avenger Ultron actually fears, however, is the Scarlet Witch. Her unpredictable hex power has defied Ultron's every attempt to formulate a counter-attack, making her the only super-hero he cannot defend himself against.
People Who Think He's Not So Bad: Under his Crimson Cowl disguise, Ultron led one version of the Masters of Evil. He has formed numerous alliances with Simon Williams' revenge-minded brother the Grim Reaper, often contributing to the Reaper's arsenal of weapons. Jocasta loves Ultron, but as much as she wants to be with him, she has trouble convincing herself that Ultron is worth compromising her morals. This lack of domestic harmony does not make Ultron any easier to get along with!
Most Despicable Act: Deciding he'd rather torture her than give her a clean death, Ultron locked the much-feared Scarlet Witch in a booby-trapped mirrored room with the intention of driving her insane. That's EVIL, pure and simple, folks!