Spender (along with his partner, Diana Fowley) was in control of the X-Files office after Fox Mulder's and Dana Scully's forced leaves in "The Beginning".

The X-Files office is concerned with cases with particularly mysterious or possibly supernatural circumstances that were left unsolved and shelved by the FBI.

But when re-appearing in the ninth season, Spender had moved on to respect and agree with Mulder's beliefs, which is proven to him in "Two Fathers", when he sees and helps to kill an alien rebel.

Posing as Mulder, he infiltrated Scully's house, and injected William with a magnetite substance to seemingly "cure" the baby of his telekinetic powers.

[2] However, as the fifth season's production period entered its final months, rumors began to circulate – especially among the production crew members in Vancouver, British Columbia, Canada – about the future of the series, particularly concerning whether the show would be moving to Los Angeles, California for the sixth season and whether the new recurring character of Jeffrey Spender was planned (in case David Duchovny cut back his commitment to the series) to become a replacement for Duchovny's character of Fox Mulder – either as a part-time or full-fledged substitute.

[12] Other, contradictory rumors that Owens heard were that either he or Duchovny would appear in only eight episodes of the sixth season and that his casting as Spender was a sign that the series would either be leaving Vancouver or staying there.

[12] According to the actor himself, he always knew that Duchovny would not be leaving the series but only discovered that The X-Files would indeed be moving to Los Angeles when the official announcement was made.

[12] According to Owens, he first learned of Spender's seeming demise in "One Son" via the usual way – when Chris Carter phoned the actor to discuss his latest script – and, upon Carter telling him that Jeffrey Spender would make an heroic exit from the series' story arc, Owens questioned himself about this news as he was slightly unable to believe that he was leaving the series so soon.

[14] Three years after Spender had been written out of the series and actor Chris Owens had moved to Toronto, Ontario, Canada, Owens received an unexpected phone call from David Duchovny, who said that The X-Files' production crew was filming the series' finale as well as another episode late in the season, and that he wanted to bring Spender back for these two episodes.