Marcus is the primary antagonist of the Pokemon film, Arceus and the Jewel of Life.
Marcus had come to resent Arceus because he feared that Arceus would turn Michina into a wasteland if the Jewel of Life was returned to it. Marcus was the real reason that Damos betrayed Arceus. He used his Bronzong's Hypnosis on Damos so that he would be under his control.
After he met Sheena, who had been sent to the past to stop Damos's betrayal to Arceus, he learned what the future would turn out to be as well as his own death. He later changed plans and decided to use silver water to kill Arceus. This proved to be very effective in wounding Arceus and causing it to be immobilized. Sheena and Damos communicated to his Heatran and Bronzong and made them turn against their master. Ash was able to make Marcus give up the Jewel of Life by wrestling with him until he dropped it. While Ash caught the jewel, Dawn, her Piplup and a group of Pokemon cornered Marcus so that he will not follow Ash.
Marcus was not defeated yet. Even though he was cornered, the other humans and Pokemon were disappearing because Arceus was close to death. Marcus explained to Dawn what was going on.
Just as all seemed lost, Damos managed to reach Arceus' heart and allow it to reabsorb the Jewel of Life and recover, thwarting Marcus' plans. Marcus' scream was heard and his crown was shown on the place where he stood, showing that he had fallen.
It does not kill him, since during the end credits, he is seen as a worker of Damos in cultivating the land.
Marcus has no powers, but he is shown to use his Pokemon for evil purposes. He also will stop at nothing to destroy Arceus.