Sebastian Derik was an agent of S.H.I.E.L.D. Derik was at some point killed in the line of duty, but was chosen to be one of the test subject for the T.A.H.I.T.I. project. Derik was revived as part of the project, but exposure to the GH.325 serum drove the test subjects insane and they became obsessed with a series of mysterious glyphs. Agent Phil Coulson, as the head of the T.A.H.I.T.I. project, came up with the idea of "erasing" them, implanting the test subjects with false memories and giving them a new identity. Derik was among the last subjects to start showing symptoms, but Coulson had him erased when he discovered Derik was carving the glyphs into his own body.
Years later, Derik had covered his body in tattoos of the glyphs. He had realized he could bring back his memories of the T.A.H.I.T.I. project by experiencing pain, and started hunting down the remaining test subjects. After killing Janice Robbins, the former Agent Rebecca Stevens, the now-Director Phil Coulson took notice of Derik's activities. However, Coulson and S.H.I.E.L.D. did not know which former T.A.H.I.T.I. test subject was doing the killings, and Coulson subjected himself to a memory machine to bring back his memories of the project. Meanwhile, Derik tracked down the only other remaining test subject, Hank Thompson, but he could not help Derik understand the carvings any further. Once Coulson had arrived at Thompson's residence and demanded at gunpoint he reveal anything he knew about the carvings, Derik was able to sneak up behind him and knock him out. Derik then tied up Coulson, Thompson, and Thompson's family in Thompson's barn where Thompson and his son had assembled a model train set. Derik started retelling his story to Coulson, but Thompson managed to cut his way out of his binds. Derik noticed he was escaping and threw his knife at him, but Thompson managed to catch it in mid-air and throw it back at him. Derik managed to dodge the knife but it cut through Coulson's bonds as well, freeing him. Derik and Coulson started fighting while Coulson tried to get Derik to realize something he had discovered about the carvings. Coulson eventually has Derik over a railing that looks down on Thompson's train set, but S.H.I.E.L.D. agents arrive on he scene to apprehend both Derik and Coulson. Fearing their director might be lost to the GH.235 serum, they pull their guns on the two of them and are prepared to shoot. Just as they are about to shoot, Derik opened his eyes and saw what Coulson was trying to show him. The carvings are meant to be viewed in three dimensions, revealing them as a blueprint for a city. With Derik subdued, he is turned over to the authorities for his crimes.
- Brian Van Holt portrays Sebastian Derik in the Marvel's Agents of S.H.I.E.L.D. episodes "A Fractured House" and "The Writing on the Wall."