Dr. Mark Desmond is an antagonist in the first season of Young Justice. He first appears in the pilot episode Independence Day and acts as the main antagonist of the first two episodes.
Desmond is the head of the secret underground facility at Cadmus Labs. There, he is breeding genomorphs who Cadmus plans to use as weapons. Desmond also uses his genomorphs to mind-controll Guardian, a superhero, whom Desmond uses as a security guard. When finding out that Cadmus has been infiltrated he sends Guardian to hunt Robin, Kid Flash and Aqualad. The three lock themselves up in the Project KR room where the find the project to be a Superman clone called superboy.
Afraid that the intruders might cause trouble or alert the Justice League, Desmond orders the activation of Superboy who, mind-controlled by the genomorphs, attacks and subdues the three intruders.
After capturing the intruders, Desmond contacts the Cadmus Leaders who refer to themselves as 'The Light'. They tell him to clone Robin, Kid Flash and Aqualad and then dispose of the real ones. While he does so, the boys are saved by Superboy. When Superboy helps the Young Justice to escape, Desmond activates every genomorph left in Cadmus to destroy the escapees. Desmond and the Guardian pursue them but are stopped when Robin hacks the motion sensors of the genomorphs. When he realises that the intruders might escape, he heads to Project Blockbuster to an his ace-in-the-hole. When he is gone, the genomorphs join Superboy in his pursuit of freedom. They are disturbed by Desmond who drinks a liquid from Project Blockbuster to 'restore order'. After drinking it he transforms into Blockbuster, a giant beast, and is promplty attacked by Superboy and Guardian. Guardian is defeated easily but Superboy manages to draw Blockbuster into a fight. During the fight, the two crash through the ceiling of the underground lab and head to the surface level of Cadmus. There, Aqualad, Robin and Kid Flash help Superboy in his fight with Blockbuster. With combined efforts they manage to defeat Blockbuster by electrocuting him and then dropping the ceiling of Cadmus Labs onto him.
After the battle, the Justice League arrive and Green Lantern, Hawkman and Hawkgirl take Blockbuster away to bring it to prison. Superman soon joins them, being uncomfortable around his clone.
Blockbuster, who has been brought to Belle Reve prison, joins in the escape attempt orchestrated by Icicle Sr.. The plan fails and he remains imprisoned. As the riot allows Professor Strange, an associate of the Light, to become the new prison warden, the Light is able to use Desmond for their plans.
On one occasion, the Light attempts to recruit Young Justice team members Superboy, Artemis and Miss Martian to their cause at Santa Prisca. They fail to convince them and a battle ensues in which Blockbuster attacks Superboy. Opposed to Superboy, who has learned to channel his anger, Blockbuster fights impulsively and is ultimately defeated.