Bill Mulder
Mulder's father, Bill Mulder, was killed by Alex Krycek, at the order of The Smoking Man. He was killed so he wouldn't tell Mulder what he knew from his years working at the Defense Department. It had appeared that Bill would confess his part in the government conspiracy to his son, but unfortunately chose that moment to go to the bathroom, where Krycek was waiting for him with a gun. Krycek has not been caught
Teena Mulder
Mulder's mother, who committed suicide in the seventh season episode "Closure". She knew things about Samantha's disappearance, but chose to take those things to her grave with her. She had a fatal disease, and decided to end her life quickly rather than cause her son the pain of watching her die slowly.
Samantha Mulder
The shocker of the series. Mulder discovered this truth in the seventh season episode "Closure". Samantha was held against her will by The Smoking Man until she was fourteen. She escaped him, but was soon to be found again, when she was taken by the "Walk-ins". These are benevolent spirits, who take children whose lives are in danger and transform them into starlight, therefore freeing them from further pain.
Scully's Father
Sorry don't remember his name! He died of natural causes early in the series. Scully saw a vision of him at the moment he was dying.
Melissa Scully
Melissa Scully was the opposite of Dana in every way. She pressed her sister to search for the truth about her abduction; while Scully was content to stay in denial. Melissa was another, although an accidental, victim of the Smoking Man. He sent Krycek and another of his pawns, Luis Cardinal, to Dana Scully's apartment one night to kill her. Unfortunately, Melissa entered the apartment instead of Dana. In the dark, Luis shot the woman, thinking she was Scully. Luis Cardinal was arrested eventually, but committed "suicide" in jail.
Deep Throat
Mulder's first informant in the X-Files investigations, he helped Mulder occasionally uncover truths he was searching for. However, he also would occasionally lead Mulder astray when Mulder got too close to something. He was killed helping Scully save Mulder's life in the first season episode "The Erlenmeyer Flask".
"X" Agent Diana Fowley Jeffrey Spender
Another of Mulder's informants, successor to Deep Throat. He was killed at the whim of the Smoking Man too, but the message he wrote in his own blood led Mulder to his next informant, Marita Covarrubias.
The first in the "Not So Dearly Departed" list. An old flame, and ex-partner of Mulder's, she returned to him in the fifth season, to the chagrin of Agent Scully. It soon became apparent, however, that she had an agenda of her own. She had Mulder committed to a mental hospital when he got sick, and stood by as the Smoking Man kidnapped Mulder to have him subjected to a surgical procedure. She had a change of heart, directing Scully to Mulder, but this led to her death.
Another FBI agent, he was put in charge of the X-Files at the demand of the Smoking Man. Jeffrey had his own reasons for hating Mulder. Mulder tried to assist Jeffrey's mother, Cassandra, when she claimed she was being repeatedly abducted by aliens. We later learned that Jeffrey was Smoking Man's son. Smoking Man shot Jeffrey dead in a fit of rage in the episode "One Son."
