While the 2004 animated series The Batman is often remembered for its radical reimagining of Gotham’s rogues' gallery—giving us a parkour-loving Joker and a beastial Riddler—it also served as the foundational stone for a new animated Justice League. At the center of that expansion was the scarlet speedster himself: The Flash.

As they moved toward the Batwing, the first support cable snapped behind them. Wally flinched. Batman didn’t look back.

: The Flash comes to Gotham to help Batman and Robin track down his hometown nemesis, Mirror Master "Lost Heroes"

He pointed to the speedster’s chest. “Your cells are overheating. The vibration that lets you phase is also tearing your mitochondria apart. In three more weeks, you’ll either burn out or phase into a concrete wall and never come out.”

3. First Appearance: “The Bat in the Belfry” (No – Actually “The Joining” – Part 1)

One common misconception: some fans think the Flash first appears in Season 4’s “The Bat in the Belfry” (a Batman vs. D.A.V.E. episode). Incorrect. The official debut of the Batman 2004 Flash is the two-part Season 4 premiere: “The Joining” (Parts 1 & 2).