Dan "The Dentist" Mendell was a member of the Group that raped Lumen Pierce. He worked as a children's dentist, under the name "Dan the Dentist", and had a wife named Laura Mendell, and a daughter, who seemed to be unaware of his dark activities.
Dan was a man in his mid 30's to early 40's with short, curly, blondish hair and somewhat of a heavyset appearance. When featured, he's shown wearing somewhat of professional office-type clothing and a tie.
Little is shown of Dan's true personality. When Dexter first meets him, he is already injured and fearing for his life after being shot by Lumen. He plays innocent long enough for Dexter and Lumen to step away to talk, but shortly after, Dexter overhears him cursing into a cell phone to another member of the group and admitting he knows who Lumen is. Once caught in his deception, Dan becomes belligerent and foul-mouthed, but this is short-lived as Dexter quickly kills him.
Mendell is one of several men who are responsible for the murder of 12 girls. Dexter originally doesn't find this information out until Mendell reveals himself through a phone call to another member of the group.
After Lumen uses her unique abilities to track him down, she fires at least five shots at him (with one bullet hitting his body) and she believes him to be dead at this point. However, he manages to get up and tries to flee the area, leaving a trail of blood that Dexter follows while illuminating some of it with Luminol. Eventually, the two of them come upon a building where the blood trail ends and they search around for him, eventually spotting him through the grating in the floor where they pull him out and begin questioning him.
Dexter looks on as Lumen and Dan argue with one another, with Dan playing the part of an innocent dentist who is also a father and husband. After a bit of a skirmish that leaves Lumen's cell phone in the building with Dan, the two of them go out and fight it over until both hear Dan talking on the cell phone to another member of the group. When they return and confront him, Mendell becomes defiant and threatening toward Lumen before Dexter snaps his neck.
Because of the sloppy way in which Mendell was killed, Dexter is unable to dispose of his body in the usual manner. Things are further complicated by another victim, Lance Robinson, whom Dexter had already drugged and left in his car after Lumen called him. As the police respond to the report of gunshots in the area, the M-99 Dexter used on Robinson wears off. Robinson panics and escapes from Dexter's car. Dexter has to quickly chase down the naked Robinson, who is still half-wrapped in plastic, as his sister and Vince Masuka quickly approach the crime scene. Mere moments before being exposed to police, Dexter catches up to Robinson and hastily strangles him and drags his body into the same room as Mendell. He takes Lumen's gun and sets it Robinson's hand just before the police arrive. Masuka investigates the scene and determines that the two men killed each other after an unusual sexual escapade turned violent. Sometime later, however, Debra uncovers Mendell's involvement with the Barrel Girls Case and The Group.
- 12 girls that were killed by Boyd Fowler and raped and tortured by him and other members of the group.
- Lance Robinson - was framed by Dexter for his murder.