Solo

Solo first appears in S2 as a strange presence in Silo 17 and nearly kills Juliette when she tries to open a vault. In episode 3, Solo, the two finally talk. He says Russell, Silo 17's head of IT, locked him in there when the uprising began, with one order: never let anyone into the vault. He claims he was Russell's shadow and tells Juliette there are dozens of silos.

The story doesn't add up. At one point he says his name was Cole Myers, but Juliette finds a staff directory, and the face of Russell's shadow isn't his. Even so, they help each other. Solo guides her through the silo and helps her go after a firefighter suit and get the water pump working. Juliette learns they aren't alone: a group of young people also survived in Silo 17. After one of their arrows wounds Juliette, she and Solo end up making peace with Audrey's group. Solo, who spent his whole life in hiding, has to learn to share the silo with other people. When Juliette heads home, he stays behind.

Solo returns in episode 8, Gray Goo. The young people of Silo 17 open the gates for Kennedy and Lukas, sent by Juliette, and Solo's group starts working with them. Solo fixes the broken radio and talks to Juliette in code. She asks where his mother sacrificed herself to hold back the poison, because she wants to do the same in Silo 18.

Patrick Kennedy's team opens a welded-shut vent and finds the body of someone in a cleaning suit with a welding rig: Solo's mother. He hesitates to move her remains. Kennedy finds him alone and explains what a burial is, something Solo has never seen. At peace, he lets the team take his mother out, and Lukas identifies the poison pipe. For the first time, Solo gets to say a proper goodbye, and his mother's sacrifice becomes the map for saving another silo.

In Hugh Howey's books, Solo appears in Wool, and Shift tells more about him. On the show, Steve Zahn plays him in S2 and returns as a guest in S3.