WARNING: The following contains spoilers for Justice League #43, by Robert Venditti, Doug Mahnke, Richard Friend, David Baron and Tom Napolitano, on sale now.
As the DC Universe's premier team of superheroes, the Justice League has confronted all manner of threats, from traditional supervillains to cosmic invaders, even supernaturally tinged myths and monsters. With such a variety of crises, the League is constantly looking to expand its roster from every corner of the DCU. In that spirit, Batman just approached one of the most powerful mystical characters on Earth for possible recruitment: Madame Xanadu.
Xanadu played a prominent role in the League's recent efforts to thwart a full-scale, planetary invasion launched by the Eradicator and his genetically enhanced forces. Xanadu was enlisted to help stop the invasion due to the Eradicator sharing Superman's vulnerability to magic. The supernatural superhero played a pivotal role in the final battle for the fate of Earth by transporting the Eradicator and his forces to a distant alien world so the League could confront them without holding back over concerns of causing collateral damage to their own planet.
As the League picked up the pieces from the recent mission, Batman approached Xanadu with the offer to become a permanent member on the team. Completely unfazed, Xanadu turned down the Dark Knight's offer to join the premier DCU ensemble, citing her continued preference for autonomy as her own superhero and hesitation to fall in line behind the rest of the team's lineup. Given Xanadu's history, this is not an entirely unexpected move, though the mystical sage has served as a prominent member on teams in the past.
Created by David Michelinie, Valerie Mayerik, and Michael William Kaluta in 1978's Doorway to Nightmare #1, Xanadu began as a tarot card reader and occultist based out of Greenwich Village -- the Manhattan neighborhood that's also home to Doctor Strange's Sanctum Sanctorum in the Marvel Universe. Xanadu helped out guests seeking their fortune, often pitting her against supernatural monsters and other things that go bump in the night. As Xanadu received her own series, it was revealed that she was actually a sorceress active since Arthurian times in medieval England.
Originally serving as a member of the Demon Knights alongside Jason Blood -- with whom she was in a romantic relationship with -- and Vandal Savage, Xanadu eventually broke out as her own hero. Across the centuries that followed, Xanadu formed a complicated dynamic with the Phantom Stranger and was responsible for bonding the Spectre to Jim Corrigan. Haunted by her actions all over the world involving the course of civilized history, Xanadu decided to open her own fortune-telling parlor and assist all that came to her for help, while also assisting supernatural heroes like the mystical Shadowpact that assembled following Spectre's rampage against magic in the DCU.
Xanadu has provided help to those who approach with genuine need but has stayed away from a committed role for centuries, only occasionally providing a more advisory role for magical threats. As one of the most powerful supernatural figures in the DCU, it makes perfect sense Batman would want her to join the Justice League, but Xanadu is likely still too haunted by her own past actions and her fiery time with the Demon Knights to commit to another team, especially one as high-profile as the Justice League. While the team can rely on Xanadu to come through when needed, a permanent role is one favor too much to ask of her.