Bio: Agent Jeffrey Spender is introduced in Patient X as an ambitious FBI agent and the mother of Cassandra Spender, an alien-abductee. Spender is against Mulder and Scully talking to his mother fearing that her stories may get him a reputation like Mulder's -- another Spooky -- and hurt his future prospects in the Bureau. This fear was accentuated by the fact that his mother had him believing that he had been abducted as a child. He now believed that he had been brainwashed by her into believing so. This sets him off on the wrong foot with Mulder and Scully. Scully even refers to him as "that little weasel" after he is assigned the X Files along with Agent Fowley replacing Mulder and Scully. Unbeknownst to either Mulder or Spender they could have an entirely different relationship. *
Despite thinking his mother is delusional and too vocal, he loves her very much and is very protective of her. Her disappearance in The Red and The Black causes him to get very upset, blaming Mulder and Scully for encouraging her belief in aliens and abduction. On her return a year later, they have an emotional reunion but it upsets him that she prefers to tell Mulder what happened to her rather than him. This she does because of another factor that comes into his life during the time she was missing.
This factor is the Cigarette Smoking Man who it turns out is Spender's father. Jeffrey never knew his father as a child and whatever his mother had told him had made him antagonistic towards the man who was his father. He returns the letters he receives from his father (The Red and The Black) and doesn't want to have much to do with him. The CSM continues to persist and manages to get Spender put in charge of the investigation into the assassination attempt on Gibson Praise (The End). Then he finally comes forward offering to help Jeffrey and finally he reveals to him that he is his father. Before a shocked Spender can react, the fire alarm goes off when Mulder's office catches fire.
Eventually persistence on CSM's part, the absence of his mother and possibly the doors he can open for him in the Bureau, lead Spender to join forces with his father. He is then assigned to the X Files along with Diana Fowley. Spender then proceeds to shred case files and eventually gets Mulder and Scully suspended for breaking into his office. Spender and Alex Krycek are sent to kill the alien rebels. Spender almost gets strangled to death during the confrontation with the rebel but is saved in the nick of time by Krycek. Krycek, himself seems to have taken it upon himself to turn Spender against his father - he gives him information on the Consortium's project and on his father's involvement with his mother's abduction. Krycek's motives for doing this are possibly a need for revenge against CSM.
Spender soon realizes he got a raw deal with his father having to deal all his father's dirty work, having to kill on command and still being found lacking compared to Fox Mulder. Also realizing there is some truth to what Mulder says, he finally recommends that Mulder and Scully be reassigned to the X Files, thus angering his father. He announces this at a meeting with Mulder, Scully, Skinner and Kersh where he also gives in his resignation. He leaves the Bureau rather abruptly, without giving two weeks' notice, turning in his parking pass, or scheduling an exit interview. During this time the alien rebels burn alive his mother and most of the Consortium and their families. He then finds out that his father was responsible for his mother's abduction and wants to pull out---at that point we see CSM raise a gun and apparently shoot his son. However we don't see any blood or a body. So Agent Jeffrey Spender could be back.

• " I'd like to build a reputation here. Not be given one." (Patient X)

• "Mulder will be back. As long as he lives, he won't give up." (The Beginning)