Dennis Gamil is the main antagonist of the Monk episode Mr. Monk and the Very Old Man.
Before the Episode
Five years before the episode starts in 1998 he was drinking and driving when he accidentally hit and killed a high school vicadictrian. He drives of and wakes up the next day to find blood and human hair on his car. He is so racked with guilt that he joins alcoholics anonymous and confesses the crime on a piece of paper which was buried in a time capsule as part of celebrating miles Hollins 110th birthday. At that ceremony the mayor promises that if miles lives another 5 years and if his still in office that the mayor would dig the time capsule up so that miles can add a last chapter. Five years later miles is nearing his 115th birthday and Dennis is scared and decides holling can't live too see his 115th birthday.
Dennis plans to kill Miles and make it look like an accident but there's one problem how can he get in the nursing home that holling lives in. He gets around this problem by stealing a security guards pass and while doing so beats the security guard to death. He disguises himself as the security guard and murders miles holling so that no one will find out about his crime. He is caught at the end of the episode and only shows remourse for the hit and run and not the murders he committed.