Giovanni Zatara and Zatanna Zatara
Coming from a long line of stage magicians who immigrated from Italy to America when his father, Luigi Zatara, was a child, Giovanni Zatara decided early to continue the family legacy. He was drafted into World War II as a young man but continued to practice stage magic when he could, often using it to entertain his comrades during rare moments of rest. While overseas, he met the Phantom Stranger, who told Giovanni he had the potential to use “real” magic, not just sleight-of-hand stage magic, and gave him a notebook written by Leonardo da Vinci, Giovanni’s ancestor. He tried to decipher the notebook but didn’t succeed until he got home and could actually focus on it, rather than using it to distract himself from the horrors of war. He spent the next decade learning all he could about real magic, falling in love with a natural magic user named Sindella, learning about the magic community though her, joining the Justice Society of America under the name “Merlin the Magician” along with his mentor Sargon the Sorcerer (John Sargent), and eventually fathering Zatanna with Sindella around 1950. Shortly after Zatanna’s birth, Sindella “died” in a car accident, leaving Giovanni to balance raising Zatanna as a single dad, being a superhero, and continuing his day job as a stage magician.
(I know he canonically never uses a superhero name, instead using his public stage name while being a superhero, but this bugs the ever loving CRAP out of me so I’m changing it. In my story, Giovanni didn’t want people to think he was “cheating” in his profession by using real magic on stage, or risk making non-magic people think they can do superhuman feats via stage magic illusions. He really wanted to keep the two separate.)
He may or may not have been cursed by the Evil Allura before he was found and saved by Zatanna and the Good Allura. Either way, this was all before the Justice League debuted, which he considered joining but ultimately decided he’s too old for this, retired from the JSA (and heroing in general), and opened a magic shop (stage magic, not real magic, though he does consult for real magic stuff on the side).
Born around 1950, around the same time Clark Kent was adopted, Zatanna Zatara was naturally gifted in magic and very passionate about learning everything to do with magic and the occult. Her father, Giovanni Zatara, kept his superhero identity a secret from her until her teens when she expressed interest in becoming a superhero. Zatanna had asked to learn more “practical” spells, like those a superhero might use, and the two danced around Giovanni’s superhero status and Zatanna’s budding desire to become a superhero before they ultimately came clean to each other, bringing them even closer as father and daughter. While he was proud of her choice, he could admit that the thought of his daughter being a superhero made him nervous. He was all too aware of how difficult and dangerous the life of a superhero was and didn't necessarily want that for his daughter, but more than that, if she was to become a superhero, he wanted it to be because she wanted to, not because she wanted his approval or felt obligated to follow in his footsteps or, heaven forbid, trying to impress a potential partner! Those were nice bonuses, sure, but he wanted to make sure the desire came from within Zatanna, not from an outside source.
Giovanni trained Zatanna for a few years and she was just starting to make a name for herself as “Zorina” when Giovanni went missing, prompting Zatanna to search for him and becoming a superhero in a trial-by-fire kind of way. He is eventually found and decides to take a step back from heroing, retiring from the JSA (slightly miffed that they didn’t help Zatanna more in finding him) and acting as Zatanna’s “sidekick”/background mentor as they work independently for a while, slowly falling back into a more consulting role rather than being out in the field himself. At some point, both of their identities had been revealed to the public but they decided to roll with it, incorporating real magic into their shows as a wow factor display and only keeping “superhero names” as a symbolic gesture to the superhero community.
By the time the Justice League debuts in 1994, Giovanni is in his 70s and really feeling his age, despite his magic keeping him young for longer than the average human. Zatanna, in her 40s, still feels like she’s in her prime and appears to be in her mid-20s; due to her mother’s magic lineage, Zatanna inherited “decelerated aging” and a long lifespan similar to Atlanteans. Zatanna happily joins the League as the Mistress of Magic and while Giovanni himself doesn't join, he agrees to consult in all matters magical and even help teach younger magic users to respect the craft. Zatanna looks maybe 30 by the time Danny is introduced to her, even though she’s in her 50s.
Sindella didn’t actually die, she was abducted by “her people”, who are a clan of magically inclined humans that call themselves “homo magi” rather than “homo sapiens”. They live in the mountains of Turkey and are similar to Atlanteans, though without their particular bias towards water-based abilities. They may also be mildly related to Themyscira, as the Amazon's language is described as a mix of classical Greek and Turkish.
I picked the name Merlin the Magician for Giovanni Zatara’s superhero name because there was a similar magic superhero by that name created shortly before Zatara debuted in DC Comics, and while this Merlin was originally made for Quality Comics, he does have ties to DC Comics and is apparently affiliated with the All-Star Squadron, which is very much a DC team. Both Merlin and Zatara were based on Mandrake the Magician, generally agreed to be the first comic book superhero as we would recognize them today, and (aside from a green cloak said to belong to King Arthur’s Merlin) both had the classic “stage magician” look with a tux/suit, mustache, and cape/capelet. Zatanna’s titles, Zorina and the Mistress of Magic, were much easier to pick, as she had apparently used them before according to the DC Wiki.