The Ultimate DC Universe is set in a player-created version of the standard DCU. Unlike the standard DC RPG, it started with no established continuity, meaning players would have to create their own origins and storylines from scratch. This allowed for much greater creativity, but also caused some hiccups in continuity.

Season 1.0:

Season 1.0 of the RPG started off fairly unassumingly, with most players working on their origin stories and without very much interaction between characters. Coupled with the fact that many elements of these stores were later retconned out, the first Season was more successful for proof-of-concept than for any major story arcs. One event in particular did bring most of the RPG's characters together--a charity event at Wayne Manor that was disrupted by the Creeper's kidnapping (and eventual murder) of Carmine Falcone.

Season 2.0:

Season 2.0 saw most of the characters really get on their proverbial feet, and several memorable storylines were set into motion. The biggest-scale event in the Season was the OMAC Invasion, wherein an army of cybernetic soldiers controlled by Brainiac attempted to overthrow the human race, only to be stopped by the combined forces of Superman, Batman, and Wonder Woman--with the additional help of The Atom, Hawkman, Zatana, and J'onn J'onzz. There was the beginning of the Untouchables, a special team of detectives set up by Captain James Gordon, and the murderous rampage of the Joker through the city. Finally, Lex Luthor revealed part of his grander schemes with the founding of the Society, and announced he would be running for President of the United States.

Season 3.0:

Thus far, the biggest event in the third Season has been the arrival of Despero, an alien being with cosmically-enhanced psychic powers. He has been tracking down the world's major superheroes and banishing them to an alternate universe--as of yet, he has captured Superman, the Flash, the Martian Manhunter, and Wonder Woman. Also of note is the massive series of attacks in Gotham City orchestrated by Two-Face, including a riot in Blackgate prison (headed by Black Mask and Scarecrow), the kidnapping of District Attourney Rachel Dawes, and a killing spree inside Gotham Central (perpetrated by the Joker)

Continuity and Retcons:

Because the Ultimate DC RPG has had various players come and go since its inception, sometimes their respective versions of characters get written out when another player wants to try their own version. This has caused a few disruptions in continuity, most notably in Season I. Some characters, such as the version of Green Arrow that was actually billionaire playboy Roy Harper, have been added into the new versions of the character in supporting roles. Some characters, such as the version of Superboy who was employed by Lex Luthor, have been written out entirely. The most recognizable victim so far has been Aquaman, who has been retconned more times than anyone else in the RPG.