One actor, multiple DC roles

[Agent Z]

Jason Spisak. Hal Jordan in DC Superhero Girls, Wally West in Young Justice, Razer in Green Lantern: The Animated Series and the Joker in Teen Titans Go.

[John Venus]

Lynda Carter: 70's Wonder Woman, Asteria in WW 88 and the President on Supergirl show.

Wentworth Miller: Deathstroke on Young Justice and later Captain Cold on CW's Flash.

Gina Torres: Vixen on JLU, Superwoman in JL: Crisis on Two Earths, Wonder Woman in DCU Online.

[Jim Kelly]

Not sure if anyone's mentioned these. Kind of general knowledge--

Lyle Talbot was Commissioner Gordon in BATMAN AND ROBIN (1949) and Lex Luthor in ATOM MAN VS. SUPERMAN (1950)--"you either die a hero or you live long enough to see yourself become the villain."

Kirk Alyn was Superman in SUPERMAN (1948) and ATOM MAN VS. SUPERMAN (1950) and Blackhawk in BLACKHAWK: FEARLESS CHAMPION OF FREEDOM (1952); then Sam Lane (father of Lois) in SUPERMAN (1978).

Noel Neill was Lois Lane in SUPERMAN (1948), ATOM MAN VS. SUPERMAN (1950) and THE ADVENTURES OF SUPERMAN (seasons 2 - 6); then Ella Lane (mother of Lois) in SUPERMAN (1978) and Alexis on an episode of SUPERBOY (1991) and Gertrude Vanderworth in SUPERMAN RETURNS (2006).

[Dr. Skeleton]

Djimon Hounsou played Papa Midnite in Constantine, King Ricou in Aquaman, and the Wizard in Shazam.

[Agent Z]

Diedrich Bader.

Zeta in The Zeta Project, Batman in Batman: The Brave & The Bold, Guy Gardner in Green Lantern: The Animated Series, Booster Gold in Justice League Action.

[Agent Z]

Grey DeLisle

* Shifter and Downpour in Justice League Unlimited

* Vulture in The Batman

* Black Canary in Batman: The Brave and The Bold

* Catwoman in the Arkham games

[Primal Slayer]

Jessica Parker Kennedy

[Frontier]

Jessica Parker Kennedy

I totally forgot about this...