Sulaiman Khan is the CEO of Castellum, Inc. He created an extremely powerful antivirus system.
Samaritan hacked into Khan's company, leaking various emails and personal details to get him fired by the company's board. Khan's subsequent quest to find who was responsible for the hack made him a number. Khan eventually came to the conclusion that an artificial intelligence infiltrated his security, after learning his company used excessive fuel and assumed it was being used for something else.
Khan was arrested for breaking into the company's server room and was targeted by Samaritan, but Reese, Finch and Root retrieved him and worked with him to locate the source of the hack. Khan was horrified to learn that Samaritan was using his code to hunt for its enemies. After Samaritan' men ambushed the team, Khan was captured and taken to Greer, who confirmed the existence of two artificial intelligences. Khan asked to "look into its [Samaritan's] eyes", prompting Greer to shoot him dead and leave his corpse staring at Samaritan's computer emblem.
Finch later explained that since the Machine's code was one-of-a-kind, Samaritan used Khan's program to search for code it didn't recognize in order to find the Machine without it noticing.