Dennis O'Copper was a State Trooper whose territory included the area near the Tiger Rest Resort and Golf Club, near the town of Haver. He was proud of his Irish heritage and often spoke with a brogue
The Tiger Lilly Case
Dennis' patrol car happened to be passing the river where Tiger Lilly had set Frizzletop and Junior adrift in a leaking canoe. He rescued the pair and took them back to the Tiger Rest. There, he helped in the rescue of Dick Tracy and the investor Mr. Chance from a second death-trap that Tiger Lilly had arranged.
Dennis continued to work with Tracy and his companions until Tiger Lilly was in custody. At the conclusion of the case, Dennis offered Tracy, Junior, and Frizzletop the use of his personal car for their return trip to the City. The car was involved in an accident which indirectly led to Tracy's involvement with Pruneface.
Dennis and Frizzletop apparently remained in contact and developed a romance. In 2012, the couple was shown to have wed. It is unclear if Frizzletop took her husband's name.
Dennis was later shown working in his capacity as a Highway Policeman at a roadblock that attempted to thwart the escape of Silver and Sprocket Nitrate. The Nitrates, after disabling the car in which Dick Tracy was pursuing them, blasted through the roadblock, firing machine guns at O'Copper and the other officers. O'Copper set aside following the fleeing criminals to see to Tracy and Sam Catchem's safety.
- O'Copper's use of expressions like "Faith!" and pronunciations of various words, such "ye" for "you," and general speech rhythm that indicates he is talking in a brogue, suggests that he is a first-generation Irishman, and presumably a naturalized American, rather than a native-born American of Irish descent.
- Since O'Copper's jurisdiction includes the North Woods (which extends from Vermont, though the Upper Peninsula of Michigan, and into Wisconsin and Minnesota), it follows that O'Copper must be a trooper in the state police or highway patrol of one of those states. Of the state police and/or highway patrols of those four states, the one with a uniform that most closely resembles O'Copper's is Michigan. Moreover, when he and Frizzletop made a brief appearance in 2012, he was wearing a uniform directly modeled on that of the Michigan State Police. Further, he was wearing lieutenant's bars on that uniform, suggesting that he had moved up in rank since last working with Tracy.
- Gould often modeled the appearance of his characters on famous people. Dennis O'Copper appears to have been based on a young Pat O'Brien, particularly the way he appeared in the 1937 film The Great O'Malley, in which he played a uniformed policeman.