Max is the father of Temperance and Russ Brennan. He took the identity of a deceased man named Matthew Brennan and changed the identities of his family to protect them from the violent bank robbers with whom he and his wife worked as career criminals. As Matthew Brennan, he worked as a science teacher, while his wife worked as a bookkeeper.
A few days before Christmas in 1991, Max and his wife left for the safety of their children and never returned to the home in order to keep Russ and Temperance hidden. After Dr. Brennan solved the murder of her mother, Max warned her to stop looking for him in a message left on her home phone.
When Russ became the target of a corrupted Deputy Director of the FBI, Max was forced to resurface and to kill the man. Max resurfaces a second time during the episode "The Killer in the Concrete," when Dr. Brennan asks for his help to find Booth, who was kidnapped during the course of the investigation.
After freeing Booth, Max escapes when his daughter willingly lets him use her car. Max was later arrested by Booth at the conclusion of "Stargazer in a Puddle". Max was tried and acquitted for the murder of Deputy Director Kirby in the episode entitled "The Verdict in the Story" (although this was only because the defense revealed that there was reasonable doubt, as his daughter suggested that she herself had motive, means, and opportunity to kill Kirby as well).
In season 4, in the episode "The Bone That Blew," Max (now going by "Max Brennan") obtained a job at Jeffersonian Institute teaching children; at first, Temperance objected to him working there, claiming he would interfere, but she finally relented, as a favor to Booth (though she knows it was for her). He asked Booth if he was sleeping with his daughter, and seemed quite surprised to learn Booth wasn't, asking whether it was because Booth was gay, Temperance wasn't attractive enough, or because her father was a killer, believing he was stopping their relationship.
In Season 5, Max reveals that he is in contact with some of his late wife's relatives, when he invites Brennan's cousin, Margaret, to Christmas dinner ("The Goop on the Girl"). He also attempts to kill Heather Taffet during her trial, when he perceives her as a threat to Dr. Brennan ("The Boy with the Answer").
This leads Booth to believe Max has not abandoned his criminal ways, and to suspect Max's involvement in two murders in Season 6 (those of Heather Taffet and a member of his bowling team), although Max is exonerated in both cases. He also indicates that he has begun dating again and that he always expected Brennan and Booth to "settle down together" ("The Bullet in the Brain").
In Season 7, he offers to take care of Booth and Brennan's daughter Christine. Despite Brennan's initial reservations, she eventually agrees. In the Season finale, he helps Brennan and Christine get out of town, after Christopher Pelant frames Brennan for the murder of her friend, Ethan Sawyer. When confronted by Booth, Max explains that Brennan has to stay outside the system, if she's to be safe. He also encourages Booth to stay in the system and help prove Brennan's innocence.
During the three months they are on the run, Max and Brennan learn all they can about Pelant, and eventually discover the grave of one of his first victims. Later on in Season 8, Max returns after Brennan is shot while working in the lab. While recovering in the hospital, Brennan gives him a message from her mother, telling Max that her mother knew that the first gift he gave to her was stolen, which takes him by surprise as no one knew that aside from him.
Birth Name: Max Keenan Aliases: Matthew Brennan Occupation: Science teacher Youth Science Guide
Family Children: Temperance and Russ Son in Law: Seeley Booth Grand-daughter: Christine Booth
Physical Description Gender: Male Hair Colour: Light brown Eye Colour: Brown
Portrayed By: Ryan O'Neal First Appearance: "Judas on a Pole" Latest Appearance: "The Woman in White"