Mark Gibbon is a Canadian actor that was actually one of the oil rig workers in Man of Steel that was rescued by Superman, Ironic now that he will be play the villain General Zod in Supergirl.
Gibbon has been on many shows such as Smallville, Arrow and The X-Files. He's also done voice acting playing parts like the Incredible Hulk, The Thing and Nick Fury for Marvel Productions.
Zod will apear in the season finale. It's not clear whether he will be set up as a villain for future seasons, or whether the appearance might happen in flashback or something like it. With both Superman and Cat Grant back for the finale, it's difficult to imagine the show has room in its runtime for anyone not directly tied to the main Rhea or Cadmus stories being the "villain of the week." For more Nerd News keep it right here at Nerds With Words