The final picture of the Marvel Villains month (sorry for being late). This time it's Ultron.
Ultron was created by Hank Pym, A.K.A. Ant-man, A.K.A. Giant-man, and other hero names.
After some encounters with the Mad Thinkers's robots, Hank Pym became interested in the robots, but found that their artificial intelligence were limited (they probably have the same IQ as a three year old child from what I understand), so therefor so did he decide that instead of creating a perfect robot, he would create the perfect AI to help him out.
The AI was named Ultron.
He did it by basing Ultron on his brain pattern (and for everyone who knows, Hank isn't exactly the most mentally stable hero in the world), and was surprised when Ultron activated itself and attacked Hank to then flee.
Hank called the Avengers to find Ultron only to find that it's working for a new super villain named Crimson Cowl.
After some fighting so did the Avengers discover that the Crimson Cowl was just Jarvis, the Avengers's butler, who was brainwashed by Ultron and used as a scapegoat.
Ultron has gone through several models and fought the Avengers on several occasions.
One time, there was even a good Ultron model who reconsiled with his father and fought by his side.
But unfortunately for heroes who uses the names of super villains, they either becomes a villain or gets killed. For this model of Ultron, an older model found him and killed him in disgust.
He also created the Vision together with Phineas Horton (the creator of the original Human Torch (who was an android) by using parts of Human Torch and the brain patterns of the then dead Avenger Wonderman.
Unfortunately for Ultron, the Vision didn't agree with Ultron's views on humans and rebelled against him.
While Ultron has mostly been exclusively an Avengers villain, so did he with the help of Super Adaptoid, and the Phalanx (an alien lifeform that's a combination of nanomachines and biological masses that can transform into anything) to conquer the Kree system.
And they were close to winning if it wasn't so that most of the cosmic heroes joined together to put wrenches in his plans.
Some of those cosmic heroes would after that war form the modern iteration of Guardians of the Galaxy.
In an alternative timeline so did Ultron take over the earth in a dystopian future.
The only way to stop him was for Wolverine and Susan Storm to travel back to the past and convince him to input a fail safe incase Ultron would go rogue (but only at a certain time).
And with the fail safe activated, Ultron was no more (as far as we know... oh wait! He did return!).

Apprearances in animated shows, and voice actors:

Avengers: United They Stand - John Stocker
Super Hero Squad - (Has apparently no voice actor)
Avengers: Earth's Mightiest Heroes - Tom Kane
Marvel Disk Wars: The Avengers - Takumi Yamazaki
Avengers Assemble - Jim Meskimen

Movies and actors:

Next Avengers: Heroes of Tomorrow - Tom Kane
Avengers: Age of Ultron - James Spader