From DC Database
Pre-Crisis is a term used to describe characters, items, realities or events that took place during DC Comics' publishing history prior to the 1985-86 Crisis on Infinite Earths limited series. The term is used by industry professionals and consumers, and is widely considered to be an out-of-universe phrase; which is to say – characters within the DC universe continuity (with rare exception), do not use the term "Pre-Crisis" when referring to events preceding the Crisis on Infinite Earths.
Compare with Post-Crisis.
The Crisis on Infinite Earths series effectively re-booted the internal DC universe from the dawn of time onward. A new history was written – one that rendered many of the older DC stories apocryphal. Characters, timelines, and events from the varying alternate realities were condensed into one modernized mainstream reality, excising many characters that would otherwise be construed as redundant.
All occurrences relating to the Golden Age or Silver Age of comic book publishing are germane to the Pre-Crisis continuity. This does not apply to stories that have been retroactively crafted to have taken place during these respective eras (ala the Silver Age comic book crossover series).
The following is a list of articles pertaining to Pre-Crisis material that is considered apocryphal, and is no longer validated in the modern continuity of DC Comics history.
- The Superman reality of Earth-Two. Although Kal-L and Lois Lane-Kent of Earth-Two survived the Crisis, their respective dimension, timeline and all related materials to the Earth-Two storyline such as the Daily Star, James Olsen, Alexei Luthor, George Taylor are no longer validated in the revised continuity of New Earth dimension, except for Power Girl. Supposedly, according to recent events somehow Power-Girl has returned to being an Earth-Two being despite the universal reset that prevented the Earth-Two reality from ever existing. The Power Girl contention has not been resolved at this time in-story.
- Superman and all-related supporting articles of Earth-One are no longer specifically validated in the revised continuity such as the current Superman was never costumed Superboy as was the Earth-One Superman. However after the events of Infinite Crisis writing and One Year Later many elements of the Earth-One history have been brought back into continuity such as the current Superman is again a three year old toddler when he arrives on Earth and not born in a birthing chamber and having superpowers from his earliest days and not developing slowly as he grew, invalidating some elements of the revised history of John Byrne's Man of Steel origin. Many of the current Superman's early adventures with the Justice League of America are similar in scope to their Pre-Crisis counterparts, but with various differences. The JLA: Year One limited series and the JLA: Incarnations limited series provides brief snapshots of Pre-Crisis JLA stories that are still considered canon.
- The Batman reality of Earth-One shares many similarities with the modern history, but with several obvious distinctions, most notably in his costume (never adopting the yellow circle emblem of the Earth-One Batman and light blue and light grey body suit) and formation as indicated in Frank Miller's Batman: Year One storyline and background as the current Wayne did NOT ever have a brother, Thomas Jr. unlike the Earth-One Batman. Wayne's personality in the modern timeline is greatly altered from that of the Earth-One continuity and many of Wayne's adventures may be considered apocryphal especially the Earth-One Batman's teamups with superpower beings such as his deep and open friendship with Superman. A clear distinction between which Pre-Crisis events survived into the modern continuity and which ones were excised has not been specifically clarified. It is safe to assume that all Earth-One Batman related material published between 1980 and 1985 may be considered canon minus obvious contradictions such as Wayne trusting Catwoman as being part of his team, while anything taking place prior to that is subject to interpretation and speculation.
- Wonder Woman and most of her related supporting articles (Steve Trevor, Etta Candy, Hippolyta etc.) of both Earth-One and Earth-Two are no longer validated in the revised continuity. All references were either eliminated or readjusted such as the Earth-Two Wonder Woman's daughter Fury being readjusted to being the daughter of the Golden Age Fury and the Golden Age Wonder Woman now being the current incarnation of Queen Hippolyta in the role. Originally in the Post-Crisis history, Black Canary (Dinah Laurel Lance) substituted for Wonder Woman in Silver Age Justice League stories. This has since been changed back to Diana as Wonder Woman being a founding member of the Justice League and involved in those adventures.
- All remaining Golden Age era characters from Earth-Two, Earth-S and Earth-X have their histories retroactively taking place on the modern Earth. Some characters have largely had their original extra Earth histories intact minus their extra-Earth events such as The Atom (Al Pratt), while others have had their entire histories completely changed such as the daughter of the Earth-Two Wonder Woman, Fury (Hypolate Trevor) and Captain Marvel (Billy Batson) never operated in the 1930s nor ever created his original supporters the Lt. Marvels unlike Captain Marvel (Earth-S), while many who originated on these other Earths now have a blendage of their original history and new elements such as Jay Garrick and Alan Scott who originally had a separate Earth history and adventures to now directly working with and at time against their same name successors along with some other background changes some minor and other major including Jay and Joan actually having a child together who died, whereas in the original Earth-Two history Jay never had any biological children at all.
- The revised history of Wonder Girl (Donna Troy) exists in a constant state of flux due to the actions of the Crisis. Donna's history was intrinsically tied to that of the Earth-One Wonder Woman, and as that continuity ceased to exist, Donna’s respective history was called into question. As such, her origin exists in a perpetual vacuum of revision. Approximately once every seven-ten years, DC Comics attempts to finalize a definitive Donna Troy origin, free of any ties to the Pre-Crisis environment.
- Johnny Thunder of Earth-One is no longer validated in the revised continuity.
- Many stories relating to Infinity Inc. can no longer be considered part of the official canon, as their background was intrinsically tied to events germane to Earth-Two. To date, a satisfactory history of the Post-Crisis Infinity Inc. history has never been provided.
There are a few characters whose existence is rooted in the Pre-Crisis alternate Earth continuity, but have survived the revisionist effects of the Crisis on Infinite Earths. See the 2006 limited series Infinite Crisis for more details.
- Most period-related Pre-Crisis material is considered a preserved part of the modern continuity. This would include characters and events pertaining to the Dark Ages, Old West, World War II etc.
- The only modern characters who have maintained memories of the Pre-Crisis timeline are: Harbinger, Per Degaton, Donna Troy, Power Girl, Psycho-Pirate (Roger Hayden) and Shazam. Presumably other characters of cosmic significance, such as Metron, likely has memories of the Pre-Crisis reality as well, but this list pertains to a confirmed list of characters only.
- To date, Per Degaton is the only character within the DC Universe who has actually used the phrase "Pre-Crisis". 
Links and References
- Alan Kistler’s Guide to the Crisis
- The Unofficial Guide to the DC Universe