The Guardian is Cadmus’s original security chief from the comics – he didn’t appear in JLU. He is the clone of James Harper, a 1940s police officer who also fought crime as the Guardian. He was created by Joe Simon and Jack Kirby and there are obvious parallels with Captain America (who the pair also created) when you see him use his shield.
The Guardian was voiced by Crispin Freeman.
The earlier part of the Guardian’s career has not been documented, but he was recognised by Robin as a known superhero. When first encountered he was the Head of Security for Mark Desmond’s Project Cadmus. The Guardian was a highly principled man who increasingly questioned Desmond’s decisions. Cadmus used an artificial species of telepathic geneomorph called gene-gnomes to provide instantaneous telepathic communication between its staff, but the Guardian was unaware that Desmond was using his gene-gnomes to suppress his descent and sway his emotions.
Desmond’s activities were revealed when Kid Flash, Aqualad, and Robin broke into the Project and liberated the Superboy. The Guardian was initially puzzled by the teen heroes presence, but was pushed to anger by his gene-gnome controller. The truth was final revealed to him when Dubbilex revealed that he had summoned the boys to Cadmus and Desmond transformed himself into the Blockbuster. Following Desmond’s removal the Guardian was promoted to lead the Project and promised Dubbilex a “kinder, gentler Cadmus” (“Independence Day”, “Fireworks” ).