Batman The Animated Series was doing well, but eventually, it became expensive to make. As well,
Superman The Animated Series was starting up, and thus a decision was made to simplify many character designs. This was a controversial move, although some characters were arguably improved (the Penguin, in particular, returned to his comic book look rather than the deformed one inspired by
Batman Returns). At the same time, the sophisticated, David Hyde Pierce-ish Riddler was transformed into Jim Carrey's decidedly less subtle version of the character from
Batman Forever.
With a Batman and Superman show airing simultaneously, the inevitable crossover occured, and the switch in art style made the cross much easier. A unified artstyle also greatly helped many of the DC Animated Universe shows later, which were either direct spinoffs of existing shows or discreetly and directly tied together.
It's generally accepted that the
DCAU includes:
...as well as the various movies and specials based on these.
A notable exception to DC-based shows being produced as part of the DCAU was
Teen Titans, which despite its radically different art and writing style, and more than a few continuity issues, has incited many a debate (or flame war) over its status as part of the 'verse. Various people on the project outright admitted it had not been written to explicitly fit into any other shows derived from
The DCU.
The
Krypto The Superdog series was another exception; however, Superman's character design in the first episode was taken from here, and unlike
Teen Titans, it has no explicit contradictions with the DC Animated Universe.
There's also the
Animated Adaptation of
The Legion Of Super Heroes, which was originally supposed to be part of the DCAU (introduced via
Poorly Disguised Pilot), but later wound up with its own continuity and art-style while still maintaining
Adaptation Distillation.
The DCAU seemed to have ended production with the final episode of
Justice League Unlimited, and at this point no plans are made to do more series in it. However, with the success of the
Ultimate Avengers direct to video release and the failure of
Superman: Brainiac Attacks, Bruce Timm's production crew is assigned to produce a number of original D2V films, adapting classic
Story Arcs from
The DCU. These include a new version of the
Teen Titans storyline "The Judas Contract", apparently to be done in the standard DCAU style.
Superman: Doomsday, adapting
The Death of Superman, has already been released and hailed as a success.
Ironically,
Freakazoid! was the first animated show to use this artstyle, yet does not fit into the DCAU for obvious reasons. The direct-to-video
Superman: Brainiac Attacks was done using the style of the DCAU and some of its voice actors, but was written by one of the producers of
The Batman and is not part of DCAU continuity.
The DCAU is sometimes referred to as the "Timmverse" (after character designer Bruce Timm) or the "Diniverse" (after writer Paul Dini). Some purists contest "Timmverse" is more appropriate, as Bruce Timm has been involved with the DCAU for a longer period of time than Paul Dini, who also left before the end of it. Rather more to the point, Dini is a writer, not a character designer. Timm, who
is a character designer, is the one responsible for the "standard DCAU art style". On the other hand, the writing of the DCAU is as notable as the art, plus the name is catchier. The debate continues.