Officer Don Orville (fullname Don Leslie Orville) is played by actor Wayne Knight. Originally a recurring character, he emerges as a series regular by the end of the show's run. As well as being the local policeman who befriends the Solomons, his character also serves as Sally's principal love interest.
In this interview, Wayne Knight discusses the role of Don Orville and his experience of being part of 3rd Rock.
Somehow Sally and Don know quite early on that they are meant for each other - from their very first encounter possibly. Sally and Don appear to be able to sense each others presence whenever they are in a room together - even before they set eyes on each other. This is particularly noticeable in an episode where she has switched bodies with Dick. Don responds in his usual manner but is somewhat disturbed to see Dick and not Sally standing beside him.
It is hard to see what the mutual attraction can be based on. In Don's case, there is the obvious physical attraction but Sally is scary to most men and for someone of Don's temperament ... ? After weighing it all up, the explanation that a woman's inability to resist the charms of a man in uniform emerges as the only plausible one. Bear in mind Sally's background as a security and weapons expert, combined with her dedication to duty in carrying out the role of 'the woman' for the mission's sake. Don's status as an officer of the law means that not only is she able to see past his inadequacies, she mostly never actually notices them in the first place, or else assumes that it represents some kind of failure on her own part - a common theme running throughout 3rd Rock.
It becomes clear quite early on that Don, in common with most of the police force of Rutherford, is lazy and incompetent. He abuses the police privileges, struggles to understand special code alerts and generally likes to avoid work as much as possible.
Periodically Don's role is that of friend to Dick. He proves in fact to be Dick's only real male friend and, apart from Mary, possibly Dick's only friend. Somehow he is not as intimidated by Dick as other people are and cares enough about him to help him by giving him advice. Don is probably the only human that Dick turns too in time of trouble. Thus he helps Dick through the period after his first break-up with Mary and Dick reciprocates when Sally and Don have their break up in season four. This is caused by Don's marriage proposal to Sally, thinking that that is what she wants him to do. The pair do get back together however and Sally even loses her virginity to him. Don really is the guy who got lucky in every sense.
Ever the girlfriend, Sally is always looking for ways to improve her man; like when she discovers that Don is not listed among the top ten most powerful men in Rutherford. She is also very self-conscious about how she compares in Don's eyes to other women. On one occasion Don drops into the Solomon's apartment to find Sally hosting a party for every woman he has ever dated.