From Nookipedia, the Animal Crossing wiki
Don Resetti (ラケットさん, Raketto-san, Mr. Racket) works for the Reset Intervention Bureau (later called Resetti Surveillance Center) with his younger brother, Mr. Resetti. He, like his brother, will give the player a small lecture about the importance of saving the game after each play. He is not as harsh and full on as his younger brother, and will merely advise the player about saving, rather than threatening them or having the player repeat sentences after him. He is a mole with stubble on his face, who wears blue overalls and a white, long sleeved shirt, which makes him appear older and mature compared to his brother. He also holds a pick-axe, which relates to his species, the mole, known for digging under ground. His name is a reference to the phrase "don't reset". He was absent in Doubutsu no Mori and Animal Crossing: Wild World.
In Animal Crossing, Don Resetti replaces his brother the seventh time the player resets. He appears mellow in comparison to his brother, by not shouting and screaming at the player for resetting. When he leaves, he does not return again and Mr. Resetti does not mention him.
Don Resetti reappears in Animal Crossing: City Folk, and his personality has not changed since Animal Crossing. He appears after the player resets five times, and after the player logs on after they first move in. He is mild mannered, and tells the player that his brother (who he refers to as "Sonny") is a good guy. Unlike Resetti, he does not yell "SCRAM!" when he ends his talk.
Don will also sometimes be present in the Resetti Surveillance Center. This can be accessed after 8:00 PM on random nights and if one of the two traffic cones are removed. Once the player enters and talk to Don or his brother, they will give the player a silver shovel to leave.
Don Resetti also appears in Animal Crossing: New Leaf. He replaces Mr. Resetti the sixth time the game is reset after the Reset Center has been built and does not appear again. If the player visits the Reset Center five times, Don will give his picture to the player.