First appearance: Fighters of Lapis 4 (as a secret boss)Latest appearance: Moon-Lords 2: Ultron's Worlds
Role in the Fighters of Lapis series
He was created to replace the Avengers, however that all went wary as he began to become aware of humanity's crimes. Created to take out humanity's biggest threat, he deemed that humanity itself was it's biggest threat and assembled a team of his own consisting of former enemies Quicksilver and Scarlet Witch and a girl named Homura Akemi. Changing the tides of time with this group, with Hawkeye only able to escape, Ultron headed out to take care of any new Avengers at the Next Avengers Tournament.
After he has been defeated in the initial timeline, he commands Homura to send him back in time again, with the Fighters of Lapis all being transported with him into this new timeline. In this new timeline, he is ruler of the world, with Ultron Cops as his police state. He is eventually defeated after the power is taken out and Tony Stark convinces him that HE is the greatest threat to humanity, shortly after being tricked by a fake Madoka trophy.
Role In The Moon-Lords Series
After being finished in the Avengers timeline, Ultron sees humanity as the biggest threat in humanity itself. It takes over half of the Earth (in the Avengers timeline.) and decides to spread his rule over to other dimensions, and recruits the help of Metal Sonic, Silver Sonic, and Mecha Sonic. At the same time, Flint Lockwood's invention, the FLDSMDFR, transported itself into a body made of Flint's old inventions, and Miku Hatsune is reborn as Miku 2.0, a kind and more forgiving version.
After Ultron becomes Ultron V.999 and flies off into space, Miku 2.0 and the FLDSMDFR fly after it and attack it. Eventually, Ultron is turned back into Ultron V.1, now destroyed. He soon realizes that HE was the biggest threat to humanity, and smashes what was left of his robotic endoskeleton on the hard pavement and dies.
Ultron is a aggressive yet cunning character who will do anything to do what he wants, even if it's killing characters permanently with the Trophy Annihilator. He used Madoka as a incentive to get Homura to take him to other timelines, and has been implied to have destroyed more than a couple Madokas in order to get Homura to do what he wanted.
He also doesn't trust others very easily, only sparing Putin because he begged for mercy. Although he saw the betrayals coming in the first timeline, he enlists only himself and Putin to fight the Fighters of Lapis in the second timeline.
Throughout the Space Crisis II, Ultron takes on many forms.