In 2373, along with his partner, Lucsly, he visited station Deep Space 9 to debrief Benjamin Sisko on a recent time travel incident, wherein Klingon spy Arne Darvin utilized the Orb of Time to take the USS Defiant back in time to 2268 in an attempt to assassinate James T. Kirk.
After the interview, Dulmur intimated to Sisko that he did not believe that the actions of his crew while in the past constituted a major violation of regulations regarding time travel, admitting that he probably would have expressed his admiration to Kirk as Sisko had done. (DS9: "Trials and Tribble-ations")
Dulmur was played by Jack Blessing.
Dulmur's name was intended to be an anagram of X-Files FBI special agent Fox Mulder's last name (Star Trek Encyclopedia 2nd ed., p. 125), though the 'e' is substituted for a 'u'. The Star Trek Customizable Card Game gives his name as Dulmer, the correct anagram to Special Agent Mulder.
In the Star Trek Online novel The Needs of the Many, at some point Dulmer contracts a time-related mental illness, and as a result has memories of numerous historical events which "never happened", including an "alternate reality" where Vulcan was destroyed in the 2250s, as well as one where a large-scale Borg attack in the early 2380s nearly destroyed the Alpha Quadrant (firmly placing the frequently inconsistent STO and Star Trek: Destiny series in separate timelines), and is institutionalized as a result. However, his psychiatric nurse, very much intrigued by his actual experience of many different universes, is Q.
Watching the Clock gives his name as Marion Frances Dulmur. It also reveals how he joined the DTI, having originally been a detective before a suspect escaped due to a temporal anomaly caused by an experiment, prompting him to track down the scientist responsible, impressing the DTI with his dedication.