Marcos (portrayed by Ron Selmour) was a minor character from the eighth season of Smallville. Appearing in the episode "Toxic", he was a criminal who had kidnapped Tess Mercer several years prior after murdering the group of marine biologists she was working with. Marcos' gang also found a poisoned Oliver Queen and had Tess nurse him back to health so they could ransom him. As the gang were about to leave on their boat, Oliver shot Marcos with an arrow covered in poison of a flower that grew on the island. Oliver and Tess boarded the boat and left Marcos to die. However, Marcos survived after finding a pool filled with leeches that fed on his poisoned blood.
Years later, Marcos came to Metropolis looking for revenge against Oliver and Tess. He found Oliver on his way to a charity fundraiser and had him poisoned with the same toxic plant that came from the island he had found Oliver on. Marcos then left for the Daily Planet, slashing Tess's tires so she couldn't escape. He assaulted Tess but Clark Kent arrived and stopped him, knocking Marcos out. Marcos was arrested by the Metropolis police, but Tess paid his bail.
As it turned out, Tess only bailed Marcos out so she could have revenge on him, thinking that jail was too good for him. As Marcos was entering a taxi, Tess appeared and smeared his hand with the toxic plant he had used on Oliver. As the poison began to take effect, Tess told the taxi driver to take Marcos to a hospital, knowing that they would likely treat him with adrenaline. However, the adrenaline would only hasten the effect of the poison, killing Marcos that much faster.