Evelyn Johnson/Eaton is Four's mother and the leader of the Factionless. She was responsible for the idea of destroying the Erudite so that Jeanine would lose control of the government, but deceived the Dauntless into believing that their goal was to restore the peace of the old faction system, when her true goal was to abolish factions.
Evelyn is described as being middle-aged with curly black hair, olive skin, a stern/angular features, hooked nose, strong jaw, spare upper lip, stick-out ears, and dark eyes that look almost black.
At one point, she met Marcus Eaton, married him and had Tobias with him. Due to Marcus' abusive nature, he often beat Evelyn. Eventually, Evelyn had an affair and left them, after Marcus attempted to exile her from Abnegation. She then faked her death, believing that their son would be safer with Marcus, despite the fact he also abused Tobias.
Evelyn convinces Tobias to become a Dauntless leader in order to ally with the Factionless. After the alliance defeats the Erudite and the traitor Dauntless, the Factionless take control of all the weapons before Tobias plays the video.
Tobias believes his mother while Tris does not.
Evelyn married Marcus and conceived Tobias. Later on in the relationship, Marcus showed his abusive nature and started beating Evelyn which led her to having an affair and leaving Tobias and her husband.
Evelyn is Tobias's mother. They have a difficult relationship due to the fact Evelyn left Abnegation, leaving Tobias at the mercy of his abusive father.
In the events of Insurgent, Evelyn appears to reunite with her son but is later revealed to have used him to gain control of the Dauntless.
In Allegiant however, when Tobias gives her the choice of continuing with the battle against the Allegiant or having her son back, she chooses her son, showing she really loves Tobias a lot.
Evelyn shows disdain for Tris saying "I am his family. I am permanent. You are only temporary." Tris does not trust her and eventually learns of Evelyn's true plans for the city.