WARNING: The following article contains spoilers for "At the Starting Line...," a story in The Flash #750 by Joshua Williamson, David Marquez, Alejandro Sanchez and Steve Wands, on sale now.
With the arrival of The New 52 in 2011, the timeline of the DC Universe was effectively rebooted, and entire swaths of continuity were simply removed, erasing characters like the Justice Society of America from the timeline. However, with DC Rebirth and later Doomsday Clock, the missing continuity has now been restored, and the JSA have been re-established as part of the main DC timeline. Now, DC is slowly revealing how the JSA fills in the gaps in DC history.
While we've already gotten some hints at this continuity in Wonder Woman #750, The Flash #750 has filled in another piece of the puzzle by firmly re-establishing Jay Garrick as DC's first Flash in the revised timeline.
Wonder Woman #750 revealed the new beginnings of the DC Universe In a short story by Scott Snyder and Bryan Hitch titled "A Brave New World," Diana Prince was established as the first public hero of the DCU at the start of World War II. Her emergence inspired Alan Scott, the first Green Lantern, to use his magic ring for good and go on to form the Justice Society of America. Essentially, in this revised timelined, by revealing herself, Wonder Woman became the first domino piece of the DC Universe.
And The Flash #750, we learn that Wonder Woman also inspired another future JSA member: Jay Garrick. The short story "At the Starting Line..." opens with a brief sequence that shows Jay gaining his superpowers in a lab, before showing the original Scarlet Speedster in action in 1940 in Keystone City. While in battle against the Thinker, Jay's narration reveals that he has had his abilities for a while, and that he has used them to help people.
However, the arrival of the heroic Wonder Woman on the worldwide stage changed things. He says the Amazon Princess showed him "we could be doing more to ensure a brighter future," and he seems well on his way to being the speedster hero who's protected the DC Universe for decades. Garrick and the rest of the JSA recently teamed up with the Justice League in the past, and a visibly aged Jay also showed up to help Superman save the world in Doomsday Clock, which suggests that he's still an active hero in the present day.
With the reveal of Wonder Woman's debut in 1939, we now know that Alan Scott and Jay Garrick were inspired to become bigger and better superheroes because of her. Her influence is likely what will lead them to form the world's first superhero team. If Diana was the spark, then Alan and Jay were the fire that would follow, and she presumably had a similar effect on DC's other early heroes.
Now that Jay Garrick has been firmly re-established as the first Flash, and a member of the larger Flash Family, it will probably only be a matter of time before he pops up again in the present day.