In previous versions of continuity, Billy’s father was named Charles Clarence Batson, named as such in honor of Captain Marvel’s creator, C.C. Beck. He and his wife Marilyn were archeologists who were hired by Dr. Thaddeus Sivana, but when Sivana’s enforcer, Theo Adam, was possessed by the spirit of Black Adam, held captive inside a pyramid for millennia, he murdered the Batsons and kidnapped the young Mary Batson. Orphaned, Billy bounced from family member to family member until he eventually gained the powers of Shazam and became Captain Marvel. He learned the truth about Black Adam’s involvement with his parents’ deaths and reunited with his long-lost sister Mary, but his father’s story was far from over.
Billy learned that his father had once helped the wizard Shazam, who was stranded in Fawcett City without his memory, and, as a result, the wizard kept a close eye on the Batson family. At one time, he even thought to grant his powers to C.C. Batson, but because Fawcett was so well-protected at the time -- with heroes such as the Bulletteer, Spy Smasher and Mister Scarlet -- it wasn’t deemed necessary. The wizard witnessed the murder of the Batsons, which is the reason he one day brought Billy Batson to the Rock of Eternity and granted him powers. All because Billy's father once helped out a scared and confused old man.
On one occasion, when Sivana altered the timestream, he changed things so that he himself was the most powerful man in Fawcett City, but in doing so he undid the deaths of C.C. and Marilyn Batson. In this altered timeline, C.C. Batson and his wife were both endowed with the power of Shazam and the wizard was faced with the dilemma of fixing the timestream at the cost of the Batson children’s happiness. Ultimately, C.C. Batson himself learned of the changes and sacrificed himself to go back in time and put things right before the damage to the timestream became too great.
Cat’s In The Cradle
While the C.C. Batson of pre-Flashpoint DC was a good egg, even in the form of a time-altered version of himself that shouldn’t exist, there’s nothing to say that the man at the end of Shazam #1 is equally as virtuous, or that he even is Billy’s father at all. It may just be a lifetime of pop culture tropes, but there’s something eerily sinister about Billy’s father returning just as Billy himself has come to love and accept his new family. Presumably, his father will want to take him away from that.
There’s also the matter of Mary to consider, as this incarnation of the character has yet to be confirmed as Billy’s biological sister. It’s possible that they are blood-related, but it’s just as likely that they’re just foster siblings. If it’s the latter, surely Billy’s father will have something to say when he learns that both his children are living under the same roof, unaware of each other's existence.
If he doesn’t say something, that may be evidence that this isn’t Billy’s father. It could be some trick of Sivana, Black Adam or any one of Shazam’s villains, and the hero himself isn’t around to see it after being transported to the Magic Lands by the Rock of Eternity. Whatever the case, when a superhero’s long-lost, thought-to-be-dead parent returns, it spells nothing but trouble.