Jennifer Jareau

"There are things we don't want to happen, but have to accept. Things we don't want to know, but have to learn. And people we can't live without but have to let go."

Jennifer Jareau is a special agent that was the BAU's former liaison with police and media officials. Upon her return in Season Seven, she officially becomes a profiler while her original position has gone to Aaron Hotchner and Penelope Garcia.

Background
JJ grew up in a small town. She graduated from East Allegheny High School near Pittsburgh, PA, where she was the captain of the varsity soccer team her senior year and earned an athletic scholarship to the University of Pittsburgh, it is also noted in Risky Business that she had a sister who committed suicide when she was young. In Season Two it is stated that she has an 8 year old niece. She is a fully qualified federal agent but has stated that she does not want to become a profiler.

Even though she wasn't a profiler for the first six seasons, she often participated in the profiling process with other members of the BAU.

Season One
Being the media/police liaison, Jennifer has spoken to the press many times in an effort to get the media to indirectly assist in investigations. She also assisted Hotch in getting information from serial killer Jacob Dawes. JJ once went on a date to a Washington Redskins game with Reid but little has come of it romantically.

Season Two
During one case, she and Reid split up at the home of the UnSub and she accidentally stumbled upon a barn full of dogs who were known to eat human flesh, while Reid was kidnapped. Though she survived by shooting them all, the event left her with brief psychological scars; at one point while washing her hands, she hallucinated that one of the dogs was behind her, and almost shot Prentiss. She seems to have recovered in subsequent episodes, though she later told Reid at another crime scene that 'no matter what happen[ed], [they weren't] going to split up.' In the episode "North Mammon" in Season 2, after playing a key role in the case, she responds to Hotch's question about if she ever thought about becoming a profiler by saying that she likes being the voice on the end of the phone that the detective or relatives of victims can talk to.

In the episode Jones she meets Detective William LaMontagne Jr. It is obvious that they are attracted to each other and at the end of the episode she gives him her number. Nothing appeared to have come to it until In Heat, when she finally showed him affection in front of the team. However, they had already known about the relationship from the beginning.

Season Three
In the episode Penelope, JJ shot Jason Clark Battle in front of FBI agents. The incident appeared to have little effect on her. In Heat revealed that she and William had been dating since Jones without her telling the rest of the team (although they had figured it out long earlier). It was revealed to the viewers in episode 3x18, The Crossing, that JJ was pregnant. New Orleans Detective William LaMontagne Jr is the father.

Season Four
JJ continued working during her pregnancy until Memoriam when she went into labor. She then went on maternity leave, her position being temporarily filled by Jordan Todd until she returned in Cold Comfort.

Season Six
When the identity of Billy Flynn is discovered by the team during his killing spree through Los Angeles, JJ is forced to act as a hostage negotiator, communicating with Flynn over the radio under Hotch's direction. JJ's speech deeply affects Flynn, who decides to release his young captive, Ellie Spicer, and commit suicide by taking a couple hostage, forcing Morgan to shoot him by threatening them.

Sometime after the Flynn case, it is revealed the Pentagon had offered JJ the position of a liaison for the Department of Defense, something she kept hidden from the team. Despite refusing the promotion twice, JJ, after a missing persons case in Maryland, is forced to take the position by "the executive branch" with neither Strauss or Hotch being able to do anything for her. At least a week later, Garcia is shown taking JJ's nameplate off the door of her old office.

JJ became part of the BAU-led interagency task force to capture Ian Doyle and briefly became a part of her old team. In the end, she is apparently one of the few people aware that Prentiss' death was faked and is seen handing her passports and bank account information in Paris, wishing her luck.

Sometime later, she presumably takes advantage of Strauss's temporary absence from the BAU as well as the FBI's budget cuts to meet up with Rossi and tell him she's "coming back".

Season Seven
In Season 7, JJ officially rejoins the team, having received the training to become a full-time profiler and field agent, instead of the Media Liaison which goes to Garcia and Hotch who divide the position between them.

When the team captures Ian Doyle and his son is kidnapped, JJ and Hotch realize that they cannot get information from Doyle without Prentiss. She is flown in as Hotch tells the rest of the team that she is alive. The team realise that Declan's mother Chloe Donaghy, is behind the kidnapping, and they manage to save Declan, though Doyle and Chloe are both killed in the process. Following this, JJ and the rest of the team were placed under investigation, though Prentiss managed to clear them.

Reid later began to avoid JJ and Prentiss as he was angry with them for not telling him she was alive. He reveals that he went to JJ's house for ten weeks after Prentiss 'died', crying, and also revealed that he had thought about taking dilaudid again. Prentiss later talked him, and he forgave her and JJ. When Will becomes a hostage to a group of bank robbers and killers, JJ becomes heavily distraught. The situation becomes even more dire when it turns out that Will unintentionally and indirectly gave away his and JJ's address, leaving Henry vulnerable as the unsubs had now gone on the run with Will as a captive. She and Rossi race to their house and she gets into a fight with one of the unsubs when she tries to kill Henry. The unsub nearly shoots her with her gun, but JJ is able to unload it before she can pull the trigger, right before subduing her. Will is later rescued and he proposes to her at the hospital. By the end of the episode, the two get married.

Season Eight
In the episode The Good Earth, JJ reveals that her grandparents owned a farm in Pennsylvania and her grandmother had to do a C-section on a cow, which ends up helping with the current case. In that same episode, JJ's son Henry doesn't want to celebrate Halloween and so she convinces him to go out by saying to find out which monsters are real and which aren't. For Halloween, Henry dresses up as Reid, "his favorite profiler".

In the episode All That Remains, JJ reveals to Blake that her sister committed suicide. She also locates a planner and several other items belonging to Judy Morrison, which the team use to clear Bruce Morrison and incarcerate his daughter. In the same episode, she is held at gunpoint by Sera Morrison before Morgan and Reid rescue her.