Madame Xanadu was a mysterious Mistress Of The Mystic Arts who ran a spooky curio shop in Greenwich Village, just around the corner from Doc Strange's place.
She was apparantly a rejig of this character, a spooky hostess Mike Kaluta had created for Forbidden Tales Of Dark Mansion and mostly just referred to as the Dark Mansion Witch.
Originally crammed into lower tier DC mystery book The Unexpected alongside a bunch of other homeless horror hosts, she got her own short-lived series in 1978, welcoming travellers into her store of mystery, and reading their fate in the Tarot cards she invariably had to hand.
Each issue was deliberately by a different creative team, which is a fun idea, but which probably contributed to the books' short 5 issue run.
Meanwhile, back at the curio shop, each issue can best be described as New York mystery romance, with Madame Xanadu portrayed as sometimes host, sometimes participant. Plus you get a superb Mike Kaulta cover each time out. It's a limited premise, but is great fun in small doses. Here's the first issue, from David Michelenie and Val Mayerik: