Mandred was created by Garguax from the bodies of his army of plastic androids on behalf of the Brain and his Brotherhood of Evil.
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History
His purpose was to kill the Doom Patrol's leader, the Chief, at a time when the core members of the team and their ally Mento were thought deceased.
Mandred was defeated by the Doom Patrol's full contingent, including the Chief, Mento and young ally Beast Boy.
The Doom Patrol kept Mandred captive, having deduced that if he was destroyed the Brotherhood of Evil would be made aware of their survival. After an inconclusive fight between the two teams, Garguax realized that Mandred needed repowering and provided it from afar, leading to Mandred's attempt at escape. He was opposed, first by the Chief and Beast Boy, and then also by the three core Doom Patrol members, but nonetheless escaped and told Garguax and the Brotherhood of Evil that Beast Boy was alive.
This revelation proved inconvenient, because the custody of Beast Boy was under dispute at the time and the Brain provided evidence that Gar Logan was Beast Boy, leading to a claim that Gar would be put under jeopardy due to his association with the Doom Patrol.
Mandred remained under Garguax's control and was still in the alien's service when he returned years later to fight the new Doom Patrol.