When is the first time you know these DC comics superheroes. For me, here is the list below for my first knowing of each heroes.
Batman = Batman the Animated Series
Superman = DCAU Justice League
Wonder Woman = DCAU Justice League
The Flash (Wally West) = DCAU Justice League
Green Lantern (John Stewart) = DCAU Justice League
Green Lantern (Hal Jordan) = Green Lantern (2011)
Martian Manhunter = DCAU Justice League
Aquaman = DCAU Justice League
Starfire = Teen Titans
Cyborg = Teen Titans
Beast Boy = Teen Titans
Raven = Teen Titans
Nightwing = Young Justice
The Flash (Barry Allen) = Young Justice
Hawkgirl = DCAU Justice League
Metamorpho = DCAU Justice League
Zatanna = JLU
Booster Gold = JLU
Black Canary = JLU
Green Arrow = JLU
Blue Beetle (Ted Kord) = Comics
Green Lantern (Kyle Rayner) = Comics
Lex Luthor = Superman's Return
Lobo = DCAU Justice League
Atom = JLU
Vixen = JLU
Captain Atom = JLU
Fire and Ice = JLU
Gorilla Grodd = DCAU Justice League
Guy Gardner = Batman: The brave and the Bold
Blue Beetle (Jaimes Reyes) = Batman: The brave and the Bold
Cheetah = DCAU Justice League
Giganta = DCAU Justice League
Batgirl = Young Justice
Jason Todd = Comics
Tim Drake = Young Justice
Damian Wayne = DCMAU
Black Lightning = Young Justice
Cassandra Cain = Comics
Katana = Suicide Squad (2016)
Deadshot = DCAU
The Flash's Rogue = DCAU
Arsenal = Teen Titans
Garth = Teen Titans
Bart Allen = Young Justice
Kon-El = Young Justice
Wonder Girl = Young Justice
Donna Troy = Comics
Animal Man = Comics
Justice Society = Comics
Stargirl = DCAU
Hawk and Dove = DCAU
Amazo = DCAU
Dr. Fate = DCAU
Mister Terrific = DCAU
Plastic Man = Batman : The Brave and the bold
Vandal Savage = DCAU
And the list goes on. Here are most of the DC heroes first interaction. Without DCAU, I won't be here with the community by knowing most of the DC heroes.