Maddox Beck is an eco-terrorist and member of the Blacklist.
Maddox and his wife, Carrie Ann, were the leaders of an eco-terrorist movement known as "The Front". Despite working together, they had very different views on their work. Carrie Ann was always the moderate of the two, preferring to only do operations directly related to the environment, but Maddox had more messianic aspirations and thought himself chosen to save the planet. The group is credited with firebombing a genomics research company in Boston in 2012 and sending ricin to the Bureau of Land Management office in Fairbanks, killing 4 people and putting 16 in a hospital. After faking their deaths when trying to bomb British Petroleum's London office, they went underground, but Maddox became increasingly radical and came to consider humanity a plague to be wiped off of the face of the earth in order to save the planet.
Beck is first seen when Carrie Ann calls Pepper, a friend from the Front, and asks for her help. Pepper shows up at their agreed meeting place, with Maddox behind her. He tries to grab something from Carrie Ann, but she runs into the street and is hit by a taxi. Beck steals what he wanted from her and leaves with Pepper. When the FBI investigate, they find 700-year-old clay under her nails, leading them to a painting stolen from Prado earlier. It turns out that the painting contains a map leading to the Apophis Strain, an old and weaponized strain of pneumonic plague. Meanwhile, Beck takes a series of infrared photos of the map.
After the bones of the priest containing the plague are tracked down to the Holy Trinity Church, the FBI go there. However, Beck has already found and excavated them when he is confronted by Elizabeth Keen. He threatens to drop the container and infect her. While she considers shooting him, she is knocked out by one of Beck's henchmen. Beck uses the bones to replicate the disease and inject them into oxygen containers fitted with breathing masks. He has a member of the movement, Sharon McManus, inhale the disease and spread it to a section of D.C.
Beck later gathers more members of the Front and has them inhale the poison, along with himself and Pepper. The plan is to send them to 24 cities spread across the globe and infect them as well. The FBI start identifying the spreaders, halting their flights and arresting the ones who haven't boarded. In the process of stopping one headed to Toronto, Samar Navabi and Liz are both infected.
Aram Mojtabai realizes that Beck's compound isn't connected to the central power grid but runs on solar power, leading the FBI to the compound. However, Raymond Reddington has figured out the same thing and goes there himself. He finds Beck and Pepper, both very much alive and well. As it turns out, Beck synthesized and antidote for himself and Pepper before spreading the plague so they could survive while the rest of the world suffered from the ensuing pandemic. Reddington tells him about a stint he served in a Russian prison when he met one of Beck's followers, who was on a hunger strike to protest an oil pipeline and eventually starved to death after 74 days without eating. He calls Beck out on his hypocrisy of sending so many others to sacrifice themselves, but staying behind himself while pretending to do the same, and suggests that his intentions may not be as sincere as he claims. He asks Pepper for the location of something and she looks at a big blue glass bottle hanging from the branch of a tree along with dozens of other colored bottles. Reddington rattles it and finds a large key inside. With sirens blaring far away, Reddington takes the plague cure and leaves Beck to his fate. By the time the authorities arrive, Beck has killed Pepper and himself.