Much of his past life is unknown, although he was friends with Billy Johnson in their childhood. During the combine occupation Dan began working for the civil protection unit as a metrocop, although unlike most of his colleagues did it to serve the city and secretly looked out for the citizens oppressed by their alien leaders. He was in secret alliance with the resistance and along with Barney Calhoun handed over intelligence on the Combine's activities.
Following the downfall of the Combine Empire and the freedom of planet earth, Dan got a job working for a legit law enforcement, starting off as a police officer. He got an assignment as an undercover cop and sent to work for the previous Combine owned City 17 Office to examine the activities and report back anything illegal. Within a couple of months of working there, he befriended Nathan Johnson, Simon Simms and reunited with Billy, with all three of the men unaware of Dan being a cop.
When Dan was unable to make progress on the "City 17 Killer" case, fellow detective Samuel Pade was sent on an undercover operation at the City 17 Office to track down the killer. Dan felt no animosity towards Samuel, as it provided him with a break.
After Samuel's retirement from the force following a harrowing ordeal at the hands of the killer, Dan was thrust back into undercover work. He began investigating criminal goings on at the office and soon discovered three newly established crime families had a stake. Along with Nathan, Simon and Billy they began working for the Angelo crime family, run by ruthless mobster Tony Angelo and worked as his enforcers. There they befriended Don Simmons. Following Tony's 'demise' at the hands of Nathan, Simmons took over as head of the family and gave Dan and his friends high-ranking roles in the family. Due to being deep within the criminal underworld, Dan was able to get his hands on their activities and feed it back to his police department, although overtime he felt guilty for 'betraying' his friends.
When the law began to close in on the criminals of the city, Dan looked for ways to prevent his friends being brought to trial or killed, so worked on a way to cut their ties from crime. When Billy nearly died when trying to set fire to his bar, Dan saved his life and came clean over his true motivations. He urged Billy to leave town for a while until things died down, in which Billy accepted.
When Simmons began to struggle within the criminal underworld during a botched drug deal which led him to be betrayed and 'dethroned' by underboss Andrew Trapani, Dan put him hiding. As the Simmons crime family began to crumble, Dan looked to bail out both Nathan and Simon. Following Nathan and Simon killing Trapani, Dan planned to put the pair of them into protection. But things appeared to fail when Simon was kidnapped by rival gangsters and seemingly killed, although Dan used a couple of close connections to rescue him and take him to a 'safe point' where Billy and Simmons were waiting. Nathan went on the run, but eventually returned to City 17 to meet with Dan and make a deal. Dan, along with Simon, Simmons and Billy, waited at the designated safe place to speak terms. But Nathan was unable to make it as when he returned to the city, two gunmen approached and shot him point blank.
Dan sent both Simon and Simmons away with new identities and to stay low for a while. Billy was appointed as Dan's right-hand man. When Dan learned of Nathan's being held at hospital, he paid off doctors to declare Nathan dead. Dan then gave Nathan a fake identity, and sent him to work in another city until the "heat" cooled down.
Thanks to Dan's efforts on taking down the crime families, he got promoted to lead detective and he appointed Billy as his partner at the precinct.
Dan started his own task force to investigate Tony Angelo, whom wasn't actually dead and now running his own trafficking empire spanning across City 17 to City 21, and other parts of Europe. Dan forged a new identity to work within Tony's organization. Dan began working with a colleague Frank Gorland, who soon turned out to be the alter ego of Frank Blackstone looking to exploit the organization for his own gain. Nathan soon returned and began working with Dan again, and the pair of them starting investigating Tony.
Brainwashing and turn to the dark side
Following the apparent downfall of the Clandestine Company and destruction of City 17, Dan returned to his special agent duties in City 16. However he was brainwashed by remaining members of the dissolved Clandestine Company, who turned him into a partial Combine prototype, revealing that their downfall was just a cover and that they are going to brainwash humanity. Dan becomes the leader of their militant task force and clamps down on citizens.
Dan leads an investigation on the disappearance of Diana Harris, who was abducted by Toby Purnell. This was part of a scheme to lure his old friend Nathan, who was in a relationship with the girl's mother Olivia. Nathan had indeed found the girl and killed Toby's dominant personality the Purple Dinosaur. Shortly afterwards Nathan was arrested by the Clandestine Task Force and taken to the City 16 headquarters, where Dan revealed himself to have turned to the other side. Nathan tried to convince his old friend that he shouldn't let go of his morals and goodness as he was the few remaining good people, but Dan refused, saying that it feels good to be on the "right" side of the fence. Dan intends not to have Nathan brainwashed into a drone like the rest of the population, but instead to be locked away and forced to live through it, showing that he has failed.
In the interrogation room Dan appears to be in contact with the mysterious Elder Supreme (leader of The Elders) who congratulates Dan on his work. Nathan breaks free from his chair and hits Dan over the head with a lamp and knocks him out. Nathan is close to murdering Dan, but holds back. Nathan takes a spare Combine uniform and makes a run for it.
Regardless of Dan's apparent change in character, it was all in fact a ruse.
- The character uses a Barney Calhoun model, with the addition of a black suit.